If you changed out all your riffles for expanded and reduced power from the motor you could work it like a pre-screened sluice, but you are going to seriously reduce the yardage per hour you can run because you will be spending so much of your time moving cobbles by hand.
Gold mining is a matter of moving material. You move more material with a sluice than a pan, and you move more with a dredge than a sluice. The larger the dredge, the more you can move. The idea is to move MORE not less. If your dredge is set up correctly, you should be capture the majority of the gold. Yes, you will lose more than with a sluice or a pan, but in working 100Xs more material you are coming out far ahead.