Unscrew the burner end.
It's hard to get at. The "burner end" doesn't screw in, in the ones I am familiar with, the hose ends in an "aerator" (for lack of a better word) and is secured by clips to the burner pan. You could accomplish the same thing by just turning on the burners and never pressing the igniter. You'd get a better build up if you don't open the lid and let the gas accumulate inside. Which is probably what someone would do if they really wanted to hurt someone.