If I use a button from e-pipe
mods, I just use a magnet under the ground plate.
As for switchs in a pipe...I just have the ground in the bottom and use 1/2 of a key ring in the top...press down and the circut is completed.
I just try to have between 2 and 5mm of vertical movement. So the battery itself is part of the circut. Basically you need a small metal plate sightly larger than the diameter of the battery hole, when you press down, it contacts the key ring which is wired to pos.
You can either have a small spring in the button or under battery.
One moving part...just following the KISS theory of electronics. More moving parts equals more chances for the wildman to mess it up.