Two ideas for you:
1) If you're putting all your feeders into the tank at one time, stop. Put them in a few at a time and when the pbass are full, add some more for the knife. Don't know if it'll for sure work for you, but it definitely worked for us when one of our pbass was eating waaaaay more than the others.
2) I have a royal knife and while he probably likes feeders best, he'll also scavenge. He's in with our catfish. He's usually a little shy, but when he's hungry he comes and takes what he wants and no one messes with him. He seems to really like smelt and shrimp (as a side note, our pbass wouldn't touch dead food if live was availible so the cut foods may be left alone by the pbass, until you have weened them off feeders anyway, so just introducing some cut food into your tank may ensure your clown knife eats).
Good luck!