Take a piece of tinfoil or metal HVAC tape and cut it about 1.5"x1.5". Take a cigarette lighter and heat it up and thumbtack it on the target as your bullseye. If you use tinfoil make it about 3-5 layers thick and it will hold the heat for a very long time. If they won't let you do that, take a surgical glove, cut a finger out and put a large ice cube in it and thumbtack that to the target. It just needs to be hot or cold, either of those ideas are simple and should work great.
Some people ask "ya but what happens when I hit the thumbtack or the ice cube/tin foil and blow it off the target?" Drop the mag, empty the chamber and call it a day. You're well within 1 MOH, "minute of hog".