Your PS3 doesn't have a disc drive at all, or it has one that's broken and won't read discs? I'm not 100% sure, but I believe that if you don't have the drive at all, you're SOL and even discless games won't work.
Also, some games not only don't work discless, but a few will even corrupt your HDD if you try to run them discless. One of the Assassin's Creed games is the primary example.