There is a large copper plane sandwiched in the middle of the Logic board near the large bad caps on a 20-inch iMac G5 and possibly similar models. It sucks the heat away. You can get a 45-watt or more nice soldering iron to deal with it. You can get a very small drill-bit (1/32' or less) and drill away the leeds for the old caps. Don't go all out and use a propane torch on the board.
