Elixir: split Genserver tasks across machines

Question

My Genserver consumer looks like so:

defmodule Consumer do
  use GenStage

  def start_link() do
    GenStage.start_link(__MODULE__, :ok)
  end

  def init(:ok) do
    {:consumer, :ok, subscribe_to: [Broadcaster]}
  end

  def handle_events(documents, _from, state) do
    for document <- documents do
      Task.async(fn -> Processor.process_document(document) end)
    end
    {:noreply, [], state}
  end

  def handle_info({_reference, {_int_state, _msg}}, state) do
    {:noreply, [], state}
  end

  def handle_info({:DOWN, _reference, :process, pid, int_state}, state) do
    {:stop, int_state, state}
  end
end

I want to "split" Processor tasks (i.e., the tasks in handle_events/3) across multiple machines if the preceding one is busy, like, waiting for a task to finish. How do I go about doing that?

I've read the guide on distributed tasks, I'm just not sure how to design it so that 1. it splits across machines, and 2. it knows when to split i.e., when it's busy:

task = Task.Supervisor.async {Something, :"server@other-machine"}, fn ->
  {:ok, node()}
end

I know it involves some arrangement like this but I'm not sure where to start. Anyone have any experience with this kinda thing?

Update

The reason I need this is that Processor.process_document(document) takes ~30 seconds to complete, and only one can be run at a time. Adding a second node capable of taking half the workload essentially halves the processing time.