I found some foot notes while looking for something else. I thought maybe they might be of some use to you... They were torn from Massage Magazine, Sept./Oct. 1997:
Exercise for the transverse arch: pick up jacks or small pebbles w/the toes, or place a towel or small rug on a slippery floor and scrunch it up inch by inch.
Then for the medial arch, I have a note that if you can relax and loosen your peroneus longus and wake up and strengthen the tibialis anterior... this is supposed to balance out the fallen medial arch...(unfortunately there aren't any notes on how to relax and loosen the peroneus longus or strengthen the tib. ant.
This isn't much of a problem over here in Hawaii. Someone once said that walking barefoot in sand prevents its occurance, but whether that is fact or fiction, I honestly don't know.