How about a Duncan P-rails? This would give you P-90 for the Special and add the single coils rails. Duncan should be able to make a P-rails that mounts like a P-90. I wonder if a dog-eared P-rails is a possibility? For switching, a 4-way blade or 4-way rotary would give you: 1. P-90. 2. Rails. 3. P-90 & Rails in parallel. 4. P-90 & Rails in series. A standard three way pickup selector would yield combinations 1, 2 & 3. A three way, like a mini toggle, could yield combinations 1, 2 & 4. I like the idea of checkerboard inlay at the 12th fret. How about square "dots" to go with that?