That depends on how you want it setup Nek, you could put some tube fittings on it with a small valve and alternate between the two systems, or you could get a T connector and "suck on both," at the same time.
I would also recommend "surgical springs" to put in the tubing so it wont kink.
If you can imagine this, this is what I would do.
Camelbak(s) -> cut off the "bite piece" on bot ->, attach a T connector to the free ends -> get about 3-6 inches of tubing, reconnect bite-piece.