You can use a "buffer zone" of trees and plants that grow well (not just resistant) with them. Most maples have no problems. Hosta do well. Nightshade plants do well (as youve seen). Mulberry can be used as well. Same with russian olive. Elderberry, hackberry, wolfberry and currents do well too. The only thing is, hackberry is also alleopathic, so watch that one (it kills grass though!)

You can also use black locust. You basically place the trees and plants around the drip line, then plant the non resistant plants outside of that drip line. THe "buffer plants" take up most of the jugalone, and make you able to grow peaches and what not near it. IF you use russian olive as part of the buffer, they nitrofy the soil, basically fertilizing it.

I was considering a zone. Basically, cut a trench, place plastic on the BW side of the trench, then backfill the trench and plant resistant plants. I was considering hybrid willows. If russian olive qualifies, certainly seaberry will qualify too, right?

The trenches wouldnt be as productive as using bearing plants, or at least ornamental.

Any Elaeagnus species should work.

This site says a bit too, namely this, but id still check it out. It lists some plant associations and communities which might give you some ideas to buffer out the jugalone:

"Black alder (Alnus glutinosa) and Russian olive (Elaeagus angustifolia)
interplanted with black walnut increases black walnut's yield because of
their ability to increase available nitrogen in the soil "

http://www.fs.fed.us/database/feis/plants/tree/jugnig/all.html