Not that I have much HSS experience, I think I'd lean towards Twinfan's suggestion of no tone on the humbucker. The only difference would be that I'm used to rewiring SSS strats to "master vol, master tone, dummy" - so I'd try to achieve the following:
Master volume
Tone for middle and neck
Dummy
Might be a little more complicated to wire up tho? If I couldn't figure it out I'd go for Twinfan's - at least you're guaranteed to find a wiring diagram for it somewhere!
I do like the idea of the "right" sort of volume pot for the singles or humbucker like badgermark's suggesting though. Trouble with this is, I am so used to a single master volume on a strat-type instrument - you might be too? For example, I still can't get used to my Explorer's controls (vol, vol, master tone, in a line). I have no problem with the standard 4 knobs on a Les Paul or SG, but for some reason my brain goes into "I'm playing a strat" when I play the Explorer, and I get very confused with the knobs... (and it doesn't help where the switch is either!!)