A month after going back to shoes, the swelling & pain manely disappeared.  Ran in sandals again & the swelling & pain returned.  It didn't return with the flip flops, only with the vibrams.  The metatarsal stress isn't from 300lbs of lion pressing down on it but from the whiplash as the toes follow behind the midpaw.  The whiplash is a much smaller force, but repeated thousands of times.  Might have to see a human doctor to finally heal the paw.  Being part human has these problems, despite being manely lion.

Ideas emerged for using thinner vibram material, adding stock EVA foam on top, & ditching the suede.  Surprisingly, the existing lace holes have held stacked materials together nicely without any heavy adhesive.