I think a heckler is one person you can get the crowd going for you if you can handle it.
Once I had a good crowd at a bar and all was well until these two airborne guys came in with this one girl. Of course they keep getting louder and louder. The way I got these guys to settle down was not in a loud voice but a very soft voice said, "behave yourself", right in the middle of a song. They both stopped dead and looked like deer in the headlights thing. Then they got loud again after a while and I said the same thing and it worked. So you could say they were apart of the act.