As godzilla_GTR mentioned, just copy your game save(s) to a USB drive, and then copy it to a new user account on their PS3... or if they want to use it under their name, replace their save with yours. They might want to copy their game save to a different user account or onto a USB drive in the event they want to keep it for later.
BTW: This is also how you can backup your game saves. Either by copying them to a USB drive and saving them on your PC, and/or setup a new user under your account, and copy your game saves to that user's account. Unlike copying to your PC, doing it this way will not protect you should your HDD fail, and not just an individual game save file.... but if you have that kind of HDD failure, saving your game saves will likely be the least of your worries.