I’m a cantor, and I agree. People are either going to join in or they won’t, but you should never have to use gestures to encourage them. You use your voice to do that, but as subtly as possible.
What’s really more important is to use your body and eyes and posture to indicate that you are praying. Not in some waving arms holy-go-pious way, either, but subtly. That way, everybody prays with you to God, instead of sitting back and watching you like you’re the show.
If you are stuck up front in everyone’s view at non-singing times, you have to stand or sit still, directing your attention to the priest (or the wall you see instead of the priest!) as strictly as possible. If you do that, people will look past you to what you’re paying attention to. In theory, anyway.
I will note, in defense of my colleagues out there, that it’s very difficult to learn to sing as a performance, and very difficult to stop performing once you learn. But it’s like any other mode of human behavior; you can shift back and forth to what’s needed at the moment. And in church, you’re there to sing as well as you can, but not to perform. You can perform for God later, if you like, at home. You are there to help worship Him.