I think you're saying that user2 should access the stick via /media/user1/stick (not /media/user2/stick) even though he/she may not know that user1 is logged in, and that user1 (who isn't here right now) should alter the permissions for the stick which user2 has just plugged in. Maybe I've misunderstood what you wrote, but that sounds crazy to me. And let's imagine that neither user1 nor user2 have any sudo privileges.
If only user2 is logged in, everything works fine, the stick is mounted at /media/user2/stick and user2 can read and write.
If only user1 is logged in, everything also works fine, just this time at /media/user1/stick.
The problem is when user1 has logged in and walked away, then user2 comes and plugs in a stick, and then neither user1 nor user2 can access it. It isn't mounted, so noone (not user1, not user2 and not any "administrator") can alter any permissions of any mounted stick. And often an "administrative user" isn't around for this quick job which (imho) shouldn't require administrator privileges.
Currently there's no fstab entry for usb stick(s), I don't think I need one, do I?
For those wondering why this "switch user" thing is important, it's because this is a laptop which often just gets its lid shut for suspend. So if somebody else picks it up and opens it, they have to use "switch user" to login. And then no USB sticks work.