What I did is lower the rear of the car inc wheels and tyres onto a couple of those blue drive-on ramps. This meant there was some weight on the rear beam but I could still get underneath to torque the bush bolts to spec.
You could use some paving slabs, bricks, breeze blocks etc - anything to support the rear wheels up in the air while you have space to crawl underneath. REMEMBER TO CHOCK THE FRONT WHEELS FIRST and leave it in gear as insurance.
If you're being pedantic there would have been less weight over the rear because it was tipped forwards at the time, but... meh. You've got to do the best you can with the tools you got.