That's exactly what is done Lee. To quote Dan's 'god-like article':
'Belt hold down roller. This too is a really easy mod that’s talked about lots on the forum and I was amazed at how much difference it has made. Basically for the belt to skip on the drive pulley the belt must physically ride up and the teeth become disengaged. By placing a roller bearing in front of the belt, if the belt tries to ride up, the bearing stops it and so the teeth can’t disengage and skip. You set it so that under normal use the bearing isn’t touching the belt causing drag, only when it would skip. I simply made mine by drilling a hole in the chassis ahead of the pulley and mounting a motor bearing on a bolt going into the belt tunnel. I’ve done this mod to a customer’s car in all of about 5 minutes!'
http://img294.imageshack.us/img294/6161/img3056ui0.jpg