I have decided to 'Channel'' the wires. Most of the process if going to be recorded at think above, but since my first patient didn't show up, I'll put a couple pics here.
The original plan was to cut a 1" channel in the foam and cover that with a foam strip. Seemed like a good idea, but in practice was a bit af a hassle. Plan 'b' may seem like more work but I think in practice it is more usefull. I took my handy dandy sharpie and marked an outline where I wanted the channel. Set my dremmel to cut 1/8" deep. Used the' router' base attachment and free handed the 1/8' recess. For a few wires 1" seemed sufficient. At times I went closer to 2".
From there took another bit-rasp type- and hogged out the channel, careful to leave a 'shelf' of recess on each side. And Viola

as you can see I cut some strips of 1/8 ply to cover the grooves. Glued in with a little titebond II and smooth over with the vinyl mud.
Since I'm sound more of a hybrid I have no danger of going all the way through the foam, unless I go crazy, since I have the inner ply layer. I'm sure this technique can be adapted to many other projects

maybe 'central air ducts'?