couple of ways you could approach this with an HSH setup
with a multipole 5 way switch you could get:
- neck hb
- one neck coil in parallel w middle sc
- one neck coil in parallel w one bridge coil
- one bridge coil in parallel w middle sc
- bridge hb
then add:
a killswitch for the middle sc to get just coil split humbuckers in pos 2 and 4
or
you could do the az partial tap for the hb's instead of the killswitch, so pos 1 and 5 will be the partially split hb's. pos 2, 3, 4 will remain the same. I'd recommend this if the hb's are low output. otherwise, full coil split is better.
This means no middle sc by itself, which I never found useful anyway, but if it's a must I can come up with some other wiring options for you to consider.