Interesting proposal there Swiffy..
I think if you got a row planter for the beans it may work best, and plant beans at a much lower population. Wider rows may give the switch longer chance at sunlight, as opposed to 7.5" rows which would close fairly quick. Then you're in trouble :)
Only problem I see is you're planting two warm season "crops" together that are competing for moisture, sunlight and nutrients at the same time. How about a cool season crop that fizzles out when the switch takes over? The annual clover + switch may not be a bad idea. Could even clip clover tops around June 1 or so above switch germination? How about spring 4010 peas instead? A little pricier, but work with your seedbox combination.
I've been contemplating cover crop possibilities for switch for some time. I've even thought of a heavy fall seeding of buckwheat and radishes on a clean seedbed, time buckwheat to flower around frost so it doesn't reseed, then frost seed switch over the winter. Residue of buckwheat + radish is minimal, both winterkill and could perhaps keep weeds at bay.. As opposed to another winterkill crop like oats - lots of residue.
Maybe even spring planted combination of winter rye or winter wheat + switch together. Doesn't vernalize.. keep mowing and it would fizzle or rust out around time switch comes on.
I've seen guys plant corn on rows + switch, as the atrazine is compatible with both. Standing stalks just add to the cover.