hi donnie,
and welcome here. you might not get a fullscale theremin into a guitar. it would be easier, putting strings on a theremin. ;-) no, seriously, there are some simple pitch only theremins that are meant to work with plate antennas. most popular and quite easy to build are the art harrison designs. link: minimum theremin. [edit]:i put some of mine into metal boxes, using the lid as attachable antenna. pictures of it on the same website. i never tried to put one into a guitar, but, hey,it probably would be doable. so you would have a theremin-like extra voice. you would like to have something for ghostly wooings? or for a controller function of, hmm, maybe a filter or so? there are some effect pedals by zvex using a plate, like a theremin for certain controls. they are a bit expensive, really, just to put into a guitar body.: pedals, you need to scroll down a bit!
i haven't seen your mentioned video, so i can't tell what's what. you can easy post links to the rest of the www. so we can see what you are up to.
frankly, it's still too early for my disasembled mind to come up with some more useful thoughts on your project, and until i haven't gathered my parts back together...(snoozing off while writing..) :-) aaah well, a last one by me: a simple killswitch (a momentary pushbutton, that takes the signal to ground) is still one of the best and so simple to do stutttututttutering fx.