If you want you can cut a piece of 20 gauge sheet aluminium or fairly thick tin can so it just wraps around the piston without overlapping, and use it with a piece of tie wire as a one-time ring compressor. It used to be fairly common practice for jobs where the ring compressor would end up around the connecting rod (in other words, any engine where you slide the cylinder over a piston with the connecting rod already attached to the crankshaft). This is because commercial ring compressors are not always suited to taking to pieces to get them off the connecting rod.
I've always used Joe's method for rings with a low tension, and the piece of aluminium if there was more ring tension. If you use the sheet metal method, be sure it's clean on the inside, and the piston is well-oiled so it won't get scratched. Don't overdo the tension on the tie-wire: remember the ring compressor has to slide down the piston.
