We use a cheap elec. fillet knife from Wal-Mart. One of us will fillet while the other one will "rib" with a paring knife. If you have one of the elec. knives with the cutting tips on the end of the blades you can also rib with them.
I've also learned that it is very beneficial to teach your partner how to use the elec.knife ....The only down side to that is sometimes I get home and my boat is gone!