Okay, somebody had the brilliant and easy idea of adding a little 'Hit RETURN' kludge to allow use of TM with svn and other external editing. So I tweaked the command line tool I posted and added a better help listing and a -w to have it block until the user hits RETURN.
I have used it successfully to check it into SVN and use TM to write the comment. The little pleasures! :)
You can get it at http://macromates.com/svn/Bundles/trunk/Scripts/tm. If you need this tool, you don't need my help installing it...
best, Eric