[Prime95]

You can put "ProofPower=5" in prime.txt. This would limit disk usage to about 32*14MB = 448MB which will go up slowly as the first-test wavefront advances.
You may also need to add "ProofPowerMult=1"

Alternatively, if you have a reasonably sized network disk drive mounted, you can ask prime95 to store the temporary files on the network disk. I do this with several of my computers.

Also: Tell prime95 to create fewer save files.