What is the proper way to run a drain for a triple bowl sink with a disposal in the middle?

A lot depends on the local Plumbing code. There is a national code as well as your local state code. If this is a commerical application I believe that each basin has to have its own trap.

answerThe "National Plumbing Code" is a MODEL code with a great name that has fooled a lot of people. (Kind of like Paris Hilton). Whether your state or municipality has adopted a code or not, this suggestion will work and pass about anywhere: On the inch-and-a-half pipe or nipple protruding from the wall install a "wye" with the branch aimed toward the far bowl, run the branch over to the p-trap on the tailpiece coming down from the strainer. Done on that side. On the straight run through the barrel of the wye, head toward the bowl on the near side. Get a "disposal kit" from the BIG BOX selling all the imported stuff. That's a straight piece of inch-and-a-half tubular with a flange on one end, and a "tee" with an internal baffle. Install the baffle tee on the vertical line between the p-trap and strainer on that second bowl, pointing it straight at the disposal outlet. The flanged piece runs from the disposal outlet to the branch of the baffle tee.