Set Check-in comment from Team Explorer plugin

I have a Team Explorer plugin that simplifies merges for our team. It lists candidate changsets then executes a merge on the selected one. After the merge, I send them to the normal Pending Changes tab to review before committing the check-in.

I really want to set the comment on the pending check-in to the comment from the original merged changeset, but I can't see how to do this. Unshelving changesets sets the comment so there must be a way to set the initial context of the PendingChanges window, but I can't find it anywhere.

Is this possible? Is there something I can pass on the line below that will set the values on the page initially?

teamExplorer.NavigateToPage(Guid.Parse(TeamExplorerPageIds.PendingChanges), [init object?]);

Thanks