there really is no way to pull the vacuum and then cap it, you would have to break the seal to put the cap on, they sell a dummy pulley that lets you remove the compressor and store it in a good environment, but thats still more money, i actually have one laying around somewhere, whether driving or not, the problem is that there is a leak, and the elements can still sneak in, and the longer its left unattended the greater the chance is of failure once he gets it back together...
seen it many times in my shop, someone has a compressor go bad and they roll with it because it still spins and just use the old school 4/60 A/C system for a while, then say a few months later get the compressor fixed, then almost always within a few more months something else with the A/C will fail, so its either fix it fast, fix it slow and replace everything serviceable then, or fix it one part at a time and keep paying for the discharge and recharge