What you can do... I've heard of it working for some people, but I personally was too busy/lazy to do it on a regular basis...
Is to take the scallop out every now and then (literature on how often to do this is sparse) give it a phytoplankton bath. Meaning put it into a smaller container with SW and put lots of plankton it. Once you feel the scallop has been fed return to tank...
This can kind of be a pain in the ***, but will definately prolong the scallop's lifetime. I'm not sure for how long though, worth a shot.