Wolf, I appreciate your sensitivity, but I don’t think there’s a problem to lip-sync on Simchas Torah, unless you do so in such a way that really draws attention to your “singing”.
In other words, moving your lips in a way that conveys you are singing loudly when in fact you are silent, seems to be an issue when viewed through this sensitivity. But merely moving your lips to the tune is a legitimate expression in joining in the simcha, just as dancing animatedly with your mouth closed would be participation.
So I don’t think it’s sheker to lip-sync at Simchas Torah as part of the kahal, because people participate in different ways, and one way of participating, in the case of a sore throat, cold or other need to protect the vocal chords, is by utilizing lip-sync. Seems okay to me.