i am not a wiring wizard by any means
but love the sounds that buckethead & t. morello do....
& yes, i was thinking along the lines of DT's modded koll guitar, and also the teuffel tesla has the same thing-i'm not sure what type of switch the tesla uses (it looks DELUXE!), i've seen it briefly in action on the henry kaiser dvd from '04 -i think he is using the microphone for feedback, and i think the 3rd switch disconnects the ground to give the 60 cycle hum (which i have on one of my guitars)
on my last 2 guitars i have been wiring the guitar pu's w/ on-off switches, i like them better than 3-way or 5-way toggles for pu selecting (i usually just have 2 pus and a mic for feedback inbetween-i'm not a big fan of the middle strat pu sound) & i find that wiring scheme easy for me (again i'm no wizard). i just use standard toggles that you can get at radio shack (electronics store in US). radioshack also sells a momentary red button that's an on-off switch-i think buckethead uses something like this on his Les Paul-the problem-it was the 1st switch i tried, and it didn't work on my guitar, i may have had a bad switch i don't know, but i'm not a big fan of that type, i prefer just using a toggle (which is what t morello uses), but buckethead's does allow for more "drumming-style tapping on & off sounds". i've seen the switch selling on ebay for like 10$, under "buckethead like toggle"-which is a joke, b/c it's like 2$ switch from radio
ALSO-check out the seymour duncan website-he has a wiring scheme as to how to put a killswitch in a guitar, basically you just mod the hot line from volume that goes to the output jack i believe, he has it laid out pretty nicely & can probably use whatever switch you feel comfortable w/...
GOOD LUCK! it is a fun mod to have & play w/ although i think b-head and t-morello do it way better than i've been able to come up w/