I have heard of guys doing this - one method was the 'rope' method. Spark plugs out, turn the crank so a piston is nearing the top of the compression stroke and feed some rope into the spark plug hole, then continue to turn the crank until the piston has been stopped by the rope. Remove the collets, take the springs out and remove the seals. Seat the new seals in with a deep socket and a couple of light taps with a hammer, reassemble, back the piston off the top of the stroke, take the rope out - rinse and repeat. I am not personally advising you to do this (I'd take the head off if it was me and inspect it) but go with what restrictions you have and what you're happy to do.