[Solved] Callback after transaction commit?

I have some code which I want to run at the conclusion of a workflow to decouple the processing from the UI user request-response cycle.

This should be straight-forward using a grid task. So at the end of my action workflow I have some code which does this:

public class InsertOrUpdateFromInterface extends AbstractActionBasedWorkflowActivity {
  ...
  public void execute(ActionBasedWorkflowContext context) {
    ...
    GridService gridService = Services.get(GridService.class);
    GridTask task = gridService.newTask(TASK_TYPE);
    task.setParams(createTaskParams(ctx).toString());
    gridService.queueTasks(QUEUE_NAME, ListUtil.create(task));
    ...
  }
}

Does GridService.queueTasks() run in its own transaction and commit immediately, or does it use the workflow's transaction?

I'm assuming it uses it's own transaction because the grid task is getting executed before the workflow and callback chain completes. 

For this requirement I need the grid task to run after the transaction commits. I thought I could do this in a Callback but it looks as though all of the methods execute within the context of the workflow/callback chain transaction. So the same issue.

How do I get the grid task to execute only after the commit has been performed?