Changing valve seals.

My friend has a 1988 Flhtc with a stock EVO engine in it . He wants to change the valve seals without having to pull the heads. He's got the rocker covers off now. I told him , back in the day, we used to take car engines and put the 1st cylinder with both valves closed and take it's spark plug out. We'd then attach an air compressor to the spark threads, with an adaptor, inflate it with air which would keep positive pressure in the cylinder and not allow the valve to move when compressing the valve springs to remove the valve "keepers ". Is there any way to do something similar on this EVO engine to change valve seals without pulling the heads? Has anyone done this?
Thanks,
Snyde

Short answer is yes, with the right tool. Check out a "V-Twin On-the-Engine Valve Spring Compressor" thingy by a basic search on the 'net.