I am guessing that you have not routed the pickups yet? I am about to do a small route to the neck pocket...I am away next week, so I'll either try it this week or the one following next week. If you have your approach sussed out, I'd love to hear it. If not, I'll post (somewhere) how I did it and how it ended up.
My basic plan is to use parts of the body that already have a hole or are routed. In my case that will be the neck pocket and the pickup routs. In your case it I would do it with a wood block clamped into the neck pocket and the pre drilled bridge holes. You could put a dowel in the hole, and a screw through it to secure the routing template platform to the wood under the bridge holes. You could screw the platform down to the wood block clamped in place in the neck pocket.
Once the platform is secure, I plan to use some wedges that I got from the big box hardware store that are normally used for leveling door frames. I will work these in place so that the platform can't rock or move. Once it can't wiggle, I'll use bungies or bicycle inner-tubes to make everything secure.
I'll use a slight modification of the routing platform template that I posted a pic of a few pages back in this thread. Anyway, FWIW it's the best idea I've had. Would love to hear your thoughts, since I know you've been noodling on the same problem.