i said that the humbucker one didn't need routing, in some control cavities it doesn't but in others it may need to have a place routed out. I would suggest that you take and do it simular to routing out a 9 volt battery, rout out the back, and have the sustainer switches in thier own cavity, then find some plastic, cut it and cover the cavity.
i think that would work better on both style guitars, ones with and without a pickguard.
routing isn't easy and if you have never done it or dont think you can, or dont have the right tools i dont recommend it. Buy a junk body first for 10$ and try it out first.