I'll be interested in the replies to this one since I had the same concerns. When I last inspected the rear control are bushings I thought through the following ideas. First, put the rear bushing on only slightly snug and do the same with the three bolts holding the bushing mount. Then have a ramp under that wheel so you can let the car weight rest on it to position the bushing at its normal angle. Mark the bushing holder and bushing with a paint line in case they move. Then jack up the front to take the weight off the wheel. Pry down on the control arm to give room for a wrench on the bushing nut. If I couldn't get a torque wrench on (starting to fantasize now), I'd planned to tighten the nut as best as I could using blue Locktite. I wonder how the Volvo engineers thought we could do this? I'll bet the same guy(s) designed the heater blower motor setup!