Hi Sam,
I think it wouldn't be quite as hard to make this information persistant if you were using Kenneth's FileManager patch. I don't know if you had any plans to implement it (it's surely a month's work to make it compatible to the latest codebase and hammer out all the bugs) but since it was serializing all FileDescs it offered easier solutions for saving that kind of information. -
It also fixed some more or less annoying quirks with the library.