So then the answer is to make the form handler do what he suggested.

Adding a drop-down combo box with "This thread","Newest Nodes", "Front Page" next to the vote button (defaulting to "This thread" to keep current behaviour) would submit the selected combo box entry along with the votes when "Vote" is clicked.

The vote-handling code could then perform the requested redirection.

Of course, I'm suggesting all this in blissful ignorance of the code base :)
--
Mike