There are all kinds of options available to you. You could add push/pull pots under your volume/tone knobs, you could add toggle switches seperate from everything and install them in a convienient part of the guitar. For simpleness sake you will need a switch per pickup ( if you are splitting all three ). So if you have a Strat style guitar with 3 volume/tone knobs, than its simple. Your top knob could be your neck pickup and so on. Each knob would be push/pull for either full or "half" humbucker. I would recommend this route. Switches are not expensive.

SD I'm sure is not the only company to have 4 wire conductor pickups, however since they are the only company I have dealt with and have done exactly what your doing, this is who I used for my example.

Don't be afraid to ask more questions. Cheers.