I'm not sure how big your groupers are, so this might not be the best idea for you...
I have a friend / co-worker that has an angler in a tank at work. We set up a tank of mollies and feed the angler those. We feed the mollies sw food. You can even convert the mollies to sw if you like, and they'll swim around longer once you put them in with your groupers. That is, if your groupers don't instantly devour them.