Usually, tighten up the adjuster on the rear brake, push down on the rear brake pedal and then loosen the bolts .
I'm not fond of using this method, but I tried it the last time I had to remove a transmission for a spline lube and when I got to the step of removing the bolts, found out I got ahead of myself .
I used a long screwdriver inserted into the 'yoke' of the u-joint got the bolts loosened up .
Can't remember if the screwdriver lodged on the frame, of if I held it, but it worked quite well .