Are the pistons still attached to the rod...if so, you might try this. Clamp the rod on a vice so that the skirt of the piston is lufsh to the top of the vice - that way the piston can not rock around. Then take your install tool and spread the ring open far enough to get the ring off the piston...just the reverse of what you would do to put them on...
Make sure you don't clamp down too hard on the rod and marr it - put something around the rod, a rag, etc.
Kirk