First, I'd go to the Yamaha motorcycle dealer and order a new part.
If you've got a traditional steel handlebar, I'd drill a small hole that matches the size and location of the tit on the throttle case.
If you've got an aluminum handlebar, I'd be a bit nervous about drilling a hole in it, so I'd probably choose to grind the throttle case tit down just enough to allow proper installation.
When done, the throttle case should still be securely mounted and not twist around. :)