You can spot feed them. Some people have been able to hand feed them as well. Feed the other fish first and then place or using a pair of tongs, wave some food in front of the BGK's hiding spot.
Mine spends all his time under the turtle dock. when I drop in minced tilapia and blood worms he comes out from under the dock and muscles the little turtles right out of the way.
It's funny to watch him steal from the turtles.