I know nothing about those tractors. Another idea, depending on how exactly the rear axle is made, you might be able to pull out the axle, which would let the rear wheels spin freely. You'd want to have a bucket to catch some oil coming out, but if it uses a floating axle (so the wheel mounts on a hub that has bearings and rides on the axle itself, and the axle is only used for propulsion), it would let you roll the tractor. It probably has an open diff, so even just removing one would let it roll.
But, it depends on the axle/diff. You want to be sure of this before undoing anything, as if it's wrong, the wheel can fall on you and then the tractor on the wheel...