The first thing would be to introduce some (more) of them. Getting a bit of sand from some established systems, grabbing the occasional critters at the LFS, etc. go a long way. Maybe even consider swapping out a piece of rock, assuming the rock doesn't pose a risk as far as die-off is concerned. The second is food. Increase your feedings and vary the types of food you feed. The best results I had were when I fed everything from things like formula 1, pellets, phytoplankton, oyster eggs, cyclops, etc. I was feeding about 3-5 times per day and very heavily.