The opposite end of that control arm is usually the one siezed in place. That is one reason to be glad I'm not in Michigan any more. Lots of rust underneath there...
Maybe try an air hammer to punch it out? Here's the general problem with this design, and you'll see it if you search. The bolt shank becomes one with the inner shank of the bushing. So you can't get the bolt out, and the bushing is still working, so it absorbs your attempts to pound the bolt out.
And, if you do get the bolt out, but damage the bushing, you'll be even worse off trying to get the outter one to remove the whole control arm.
My advice, though its probably not what you want to hear, would be to pick up two new rear control arms, hardware, and swaybar end links, then go to town with a cut off wheel.
Parking Lot Hero
2008 WRX daily driver
2003 ZX3 23D Autox Car 42 FSP
"Hella Functional - Raced, Not Hard Parked"