Warm them up good (in front of a heater, over a furnace register, etc.) and put some dish soap or tire soap on them. Place tire flat on concrete, insert rim and use both feet to step on opposite edges. Put other rim half on ground and place the rim/tire over it and again walk on the tire/rim. Be sure to line the holes up first or you will get to do it again. If holes are off half a hole insert one to four punches and the rim will shift around.

John