All I know is wilting is the result of more water going out (transpiration) than coming in(osmosis). to prevent it you need to either lessen transpiration(increase humidity or somehow clog the leaf pores) or increase osmosis (maybe keep roots wrapped in or laying on a wet towel).
That's why grocery stores all have those little sprayer set-ups in the produce department and your leafy veggies are always wet when you buy them.

This might seem a bit of a commercial solution, but have you tried ziploc vegetable bags. They have tiny performations in them so the bag breathes, but it keeps in moisture well, and seems to keep my store-bought lettuce fresh (well, as fresh as store-bought gets). Just a thought.

We keep lettuce heads in a bowl of cold water in the fridge. Lasts for several days.