Harbor Freight sells a strap wrench where the strap is a vee-belt. I use it to hold pulleys still, and to turn some engines for valve adjustment. Very handy.
Thanks for all the suggestions. I have a DeWalt impact wrench and just picked up a 30mm socket to try the next time I'm up in the mtns where the tractor is. I thought about using a carpenters clamp to pinch the belt real tight together just on the other side of the pulley.