Here's another option:
Take some thin wire lead free solder (radio shack) and wrap a few
coils around the tip of a pair of tweezers making a ball. Press the ball of solder into the
threaded section of the button cap. Because it's so soft and pliable it won't damage the
threads and will mold itself when you screw in the plunger. Also, it's easy to remove if you get tired of it.
More makes the button higher....less for lower. When you get the height where you want it, assemble the switch, give it a good twist so it's good and tight, and put it on the tube. Just make sure you don't make the button top too high otherwise the knurled locking ring will unscrew before it locks.
It's invisible, removable, and doesn't damage the switch.