Can I update Sale vs. Original Price data, in my Shopify Google Merchant Center feed, via a simple change in the product schema file?

Question

On my Shopify Store, I use the Google sales channel app to automatically create a Merchant Center Feed for all my products.

When I run sales on my website, I don't actually bulk-update all of the original vs. compare at prices for the products, since I have thousands of variants and it would take forever. Instead I use a simple code switch that will conditionally display the appropriate sale prices to users (then auto-apply a discount for that amount at checkout).

The problem is, this doesn't push the sale info to the Merchant Center Feed, since I don't actually change the underlying prices.

What I'm wondering is, could I modify the schema that's sent to / read by Google, when it creates the Merchant Center Feed for my products, to conditionally display the sale vs. original prices?

Here's my v1 attempt at this:

{% assign current_datetime = 'now' | date: '%m-%d-%Y %H:%M' %}
{% assign SaleStartingDatetime = 'REPLACE_THIS_WITH_SALE_STARTING_DATETIME' | date: "%m-%d-%Y %H:%M" %}
{% assign SaleEndingDatetime = 'REPLACE_THIS_WITH_SALE_ENDING_DATETIME' | date: "%m-%d-%Y %H:%M" %}

{% if current_datetime >= SaleStartingDatetime and current_datetime <= SaleEndingDatetime %}
  {% assign SaleActive = true %}
{% else %}
  {% assign SaleActive = false %}
{% endif %}

{% assign SaleDiscount = REPLACE_THIS_WITH_SALE_DISCOUNT %}
{% assign SaleMultiplier = 1.00 | minus: SaleDiscount %}

{% assign SaleStartingDatetimeConverted = SaleStartingDatetime | date: "%Y-%m-%d %H:%M" %}
{% assign SaleEndingDatetimeConverted = SaleEndingDatetime | date: "%Y-%m-%d %H:%M" %}

{%- assign selected_variant = product.selected_or_first_available_variant | default: product.variants.first -%}
{%- assign product_image = selected_variant.featured_image | default: product.featured_image -%}

{%- capture product_name -%}
  {{ product.title }}
  {%- if selected_variant.title != 'Default Title' and selected_variant.option1 == 'Default Title' -%}
  - {{ selected_variant.title }}
  {%- endif -%}
{%- endcapture -%}

{%- assign now = 'now' | date: '%Y-%m-%d' | split: '-' -%}

{% capture year_from_now %}
  {{ now[0] | plus: 1 }}-{{ now[1] }}-{{ now[2] | at_most: 28 }}
{% endcapture %}

<script type="application/ld+json">
  {
    "@context": "http://schema.org/",
    "@type": "Product",
    "name": {{ product.title | append: ' - Canvas Wall Art' | strip_newlines | json }},
    "image": {{ product_image | img_url: '1024x1024' | prepend: 'https:' | json }},
    {% if product.description != blank %}
      "description": {{ product.description | json }},
    {% endif %}
    {% if product.vendor %}
      "brand": {
        "@type": "Thing",
        "name": {{ product.vendor | json }}
      },
    {% endif %}
    {% if selected_variant.sku != blank %}
      "sku": {{ selected_variant.sku | json }},
    {% endif %}
    {% if selected_variant.barcode != blank %}
      "mpn": {{ selected_variant.barcode | json }},
    {% endif %}
    {% if SaleActive == true %}
    "offers": {
      "@type": "Offer",
      "priceCurrency": {{ cart.currency.iso_code | json }},
      "price": {{ selected_variant.price | times: SaleMultiplier | divided_by: 100.0 | json }},
      "availability": "http://schema.org/{% if selected_variant.available %}InStock{% else %}OutOfStock{% endif %}",
      "url": "{{ shop.url }}{{ selected_variant.url }}",
      "seller": {
        "@type": "Organization",
        "name": {{ shop.name | json }}
      },
      "priceValidUntil": "{{ SaleEndingDatetimeConverted }}"
    }
    {% elsif SaleActive == false %}
    "offers": {
      "@type": "Offer",
      "priceCurrency": {{ cart.currency.iso_code | json }},
      "price": {{ selected_variant.price | divided_by: 100.0 | json }},
      "availability": "http://schema.org/{% if selected_variant.available %}InStock{% else %}OutOfStock{% endif %}",
      "url": "{{ shop.url }}{{ selected_variant.url }}",
      "seller": {
        "@type": "Organization",
        "name": {{ shop.name | json }}
      },
      "priceValidUntil": {{ year_from_now | json }}
    }
    {% endif %}      
  }
</script>

While this would apparently update the product prices (based on a Rich Results website tester), there's nothing in that that specifies: "Here is the original price, here is the current sale price", so it can show the comparison and display the savings to people.

Is there some simple additional parameter I can put inside of there to specify that? Something like "compare_price"? Or alternatively, is there some OTHER schema section that Google reads this information from, to create its Merchant Center Feed?

I have the Google sales channel / app on my Shopify Store. It automatically creates the Merchant Center feed for all products and variants on my store. Here's the critical question that may allow me to achieve my goals via a simple code switch: How does Google actually READ this information from my Shopify Store? Where, specifically, does it GET the information about, the current price, vs. the original compare at price -- to output this via the Shopping Ads / Merchant Center Listings Feed? Because it has to read that information from SOMEWHERE in my theme file code, right? And it follows that, if I just find where exactly it reads it from, I could modify the information accordingly to display both the sale price and the original price, during the specified time period of the active sale?

Otherwise I'd hate to have to manually piece together some super long XML feed just to be able to pass this info to Google Merchant Center whenever we're running a sale. I'd prefer to just, indicate to them: "Here's the current sale, adjust all prices accordingly" via a simple code switch of some kind, at the pertinent locations where Google crawls and gathers this information from the website.

Thanks!