#1
So, I'm going to get a killswitch put in my Gibson Les Paul w/ 3 p90 pickups.

Simple question, where should I put it on the body? Its being done professionally and its a momentary push button.

Cheers

PS wondered if it would be possible to get it it the hollow section of my guitar's tone control knob? Or is this just mental and couldnt be done?
#2
I don't think the tone knob idea will work. look up a pic of a tone pot on google image search. That'll give you an idea of why that won't work.

I used to have one on my guitar. Open up the back cover on your guitar. You'll notice that there's a cavity in your body where the backs of the tone/volume pots as well as the wiring sits. The best place to put the killswitch (and really the only unless you're looking to have someone cut a new cavity into your guitar somewhere) is coming through the body somewhere in that cavity. If I were you I'd make a note of where your hand typically is when you're strumming and try to get it as close to that area as possible (i.e. in reach) but without the possibility of you accidentally running into it while you strum. You want it to be accessible so that you're not reaching too far from where you usually strum to use it.
#3
As to avoid any uneccessary routing, I'd ditch the momentary switch and go for a push/pull instead--use it in any of the existing 4 pots.
Oh, frack! But, I didn't say frack--I said "THE" word. The F-dash-dash-dash-dash word.
#4
If you don't really use your tone pot, i'd just have it in the actual cavity and then put the kill switch in the tone pot hole. that way you wouldn't have to drill a hole in your gibby. Or drill a hole, your choice.