I was thinking of the potential for mold. Baking the bread bedding to about the same level of dryness of oatmeal. But if they could process it quick enough then that wouldn't be a problem. How quick could they eat a slice do you think?
Perhaps start with a layer of the dried bread crumbs and then just leave bread slices on the top with an apple slice or something?
I think if you do one layer let it completely air dry and then do the next layer on top let it completely air dry, etc.. you won't have a mold problem. The worms will tunnel through it and eat it both moist and dry. The dry air combined w/ the little water suckers (mealies) should dry it completely long before it has a chance to mold. But when you start I would keep a close eye on it just in case. There may be an added benefit of no mites to have to be frozen or nuked.