I saw somebody on FBBO that welded up a tool to do this. Basically, it's a metal plate, maybe 5"x6"or so with holes drilled into it that line up with the pinion yoke. It also had a large hole cut in the center to allow access to the pinion bolt.

That plate is welded to a 3ft. bar. You use the rear u-joint bolts (or u-bolts) to bolt to the plate, lift the car slightly so you can get under it, torque (or impact) the pinion bolt & the long bar hits the ground so the rear yoke can't turn.

I've never seen one for sale, just this home-built one.