Well, it depends on the variety of gremlin...I think for Soapus Escapus gremlins (missing ingredients) such as your problem, just literally singing the lyrics backwards will suffice ("Are you what wonder...").
However, for the more tricksy wee buggers, like Soapus Stickus Gremlins (responsible for seizing in the pot), you would certainly have to sing the lyrics and actual words backwards ("Era uoy tahw rednow...").