You beat me to it Dennis, the factory copper washers are still intact. That's what's keeping the third member in. You're method might work, but it'll take quite a while since the fluid is so thick and he doesn't mention if he's in a heated garage in Minnesota. I'd add to that idea though, I have a bendable magnetic tool, after whacking, I'd take the nut off completely and put the magnet on the tip of the bolt and press it thru the hole. Once all the fluid is drained, pull it back into the hole after you've cut the old copper washer with a chisel and pulled it off.
That being said, I've always been one to want to remove the center section to visually inspect the inside of the thing. It would suck not to do this, then have a catestrophic failure later and have to do it again, you never know what you might catch, plus you get a chance to inspect your wheel bearings and rear brakes and it might not be a bad idea to put in new axle seals.