Now you got me thinking about how to hide the GK "box" under the pickguard of my SE EG and still have access to the controls (if I even need those).
What you need is one of these:
You can fit as many or as few of the controls as you want. I have one in an SE Custom 24. I replaced the tone pot with the GK pot and fitted two mini-toggles - one for patch up/down and one for guitar/synth selection. You do need to make a pretty big hole for the jack though. They're pricey in the USA, but are only about £70/$110 in Europe.