That would work, you'd just set the pickup height to balance the bridge and neck out. Or you could use 3 volumes and a master tone. It depends on how much independent control you need. You're going to probably at least need the separate controls for the middle, since it'll sound more different than the neck and bridge will from each other(assuming you use the same kind of pickups). To me, the most sensible control scheme would be 4 push-pulls: 1. Volume for neck, 500k, with pull for coil split; 2. Volume for middle, 250k, with pull for middle on; 3. Volume for bridge, 500k, with pull for coil split; 4. Master tone, 500k, with pull for middle-only output. If you'd rather have switches, you could do that instead of pulls. It'd be nice to have a way to have only the middle selected, though. The three volumes give you more control over blending, and the middle bypass would work whether you had the middle on or not.
I just suggested the switch plate because I'm a switch junkie, but now I'm thinking that might be kind of silly to try to do on a Les Paul.