Someone gave me the brilliant idea of hot sauce for my son when he was having a problem with biting. It was great. It scorched the inside of his mouth. :-( Didn't exactly make me feel like Mother of the Year.
Vinegar worked for us, and still does, for biting and "potty mouth" problems. It's just nasty, and the kids don't like it. Even the smell helps them straighten up quickly, and we have rarely actually had to put it in their mouths.
The only thing to consider... is there maybe a REASON he's doing it? Self-stimulation, self-regulation, self-soothing etc.?
My son has multiple special needs, and finger/hand/thumb sucking are ways he self-regulates when he's feeling overloaded. Punishing him for that would be wrong.
You said he's not sucking them, but I might be curious about his need to do it at all. Is he only doing it when he's tired/angry/upset/overloaded? Or is he doing it unconsciously or just to get a rouse out of you? It matters why, I believe.
Anyway, good luck. Ain't being a parent THE MOST FUN? Hee hee. (Someday we'll look back like our parents and wonder why it is that our kids have such a difficult time... it's EASY, right?!)