I have an idea that might work...and it's kind of a "first step" approach...essentially follows this comment:
I vote vol/vol with the Dimarzio wired fullbore. You lose the coil splitting ability but I bet you can get lots of cool sound just by blending the two pups.
...What do you think of installing two pots, each with a push-pull switch, each pickup full output? I could then switch each pickup on/off. The push-pull would allow traditional style EB knobs.
...Or I could do a stack-knob setup for vol/tone on each, with the ability to use the vol function to turn each pickup up or down. This would necessitate a non-EB style set of knobs...but this appeals to me the most of the two options.
What do I lose? the ability to split the coils, but I have all the ability to balance the two pickups and vary tone.
And no new holes.
If the result isn't satisfactory, I could do further mods....including such an idea as a slider switch on the back cover to do coil switching.