One other thing that comes to mind - the further forward you trapeze will reduce the side force on the traveler as you sheet in. Perhaps you are trapping too far back?
Giving the sheet to the crew would reduce side force. The only time I've ever noticed the traveler moving was when the skipper had it and he was really cranking down hard on the sheet. Like Jake said, it slid right back into position.
If I understand the drawing (which I probably don't) you would have to release and reset the traveler on every tack/gybe which is just another thing to worry about.
-Rob V.
