How to combine summary row and sparkline in a gt table?

Question

I would like to have sparkline charts from the gtExtras package not only for my data rows but also for the summary rows in a gt table. Is this possible? So far i have sparklines only for the raw-data-rows but not for the (grand)-summary:

library(tidyverse)
library(gt)
library(gtExtras)

these_years <- c(1980,1990,2000)

df <- countrypops |>
  dplyr::filter(country_code_2 %in% c("BE", "NL", "LU",
                                      "DK", "SE", "NO"),
                year %in% these_years) |>
  dplyr::mutate(region = ifelse(country_code_2 %in% c("BE", "NL", "LU"),
                         "Benelux",
                         "Scandinavia")) |> 
  dplyr::select(region, country_name, year, population) |>
  tidyr::pivot_wider(names_from = year, values_from = population) 

df |> 
  mutate(trend = list(c_across(where(is.numeric))), .by = country_name) |> 
  gt(
    rowname_col = "country_name",
    groupname_col = "region"
  ) |>
    summary_rows(
    groups = everything(),
    columns = num_range(prefix = "", these_years),
    fns = list(
      Sum =  ~ sum(., na.rm = TRUE)
    )
  ) |> 
  grand_summary_rows(
    columns = num_range(prefix = "", these_years),
    fns = list(
      Grand_Sum =  ~ sum(., na.rm = TRUE)
    ),
    side = c("bottom"),
    missing_text = "---"
  ) |> 
  gtExtras::gt_plt_sparkline(
    column = trend,
    palette = c("grey40", "grey40", "grey40", "dodgerblue1", "grey40"),
    type = "points",
    same_limit = FALSE
  )

This is what I get

But i would like to have the sparklines in the summary rows as well: This is what I want

I know that it would be possible to add the lines manually by adding the (grand-)summary line before generating the trend column and adding some horizontal lines for the look:

df |> 
   bind_rows(df |> 
              pivot_longer(cols = -c(region, country_name),
                           names_to = "year",
                           values_to = "value") |>
              summarise(total = sum(value), .by = c(region, year)) |> 
              pivot_wider(names_from = year,
                          values_from = total) |> 
              mutate(country_name = "Sum"),
            df |> 
              pivot_longer(cols = -c(region, country_name),
                           names_to = "year",
                           values_to = "value") |>
              summarise(total = sum(value), .by = c(year)) |> 
              pivot_wider(names_from = year,
                          values_from = total) |> 
              mutate(country_name = "Grand_Sum",
                     region = "")) |> 
  mutate(trend = list(c_across(where(is.numeric))), .by = country_name) |> 
  gt(
    #rowname_col = "country_name",
    groupname_col = "region"
  ) |>
  tab_style(
    style = cell_borders(
      sides = c("top", "bottom"),
      weight = px(1.5),
      style = "solid"
    ),
    locations = cells_body(rows = country_name == "Sum")
  ) |> 
  gtExtras::gt_plt_sparkline(
    column = trend
  )