I made a valve compressor after renting one from an auto store. It was much quicker and not difficult....
spark plug socket
So to remove a valve cap from the stem I used a spark plug socket with a rectangular magnet which fit in the spark plug socket. Then I used vie grips to act as handles to connect to the spark plug wrench for placement. I placed the 2x4 under a vice to use as leverage to compress the spring. The magnet was on top of the valve and as you compress the spring and the retaining locks were free'd the magnet would attach to them and you release the 2x4 the retaining locks were on the magnet.
To reinstall you place the components back into the seat and the retaining locks carefully seat as close to normal as possible. Then fold a ziplock bag 4 or so times so that the metal doesn't puncture the bag. Then place spark plug socket on top on the bag and apply leverage with 2x4. Get the hang of it. It works pretty well:)