Managed Mode: Alternate folder structure in case of missing tags?

Is there a way to have Songbird use an alternate folder organization for Managed Mode, if the tags you tell it to use are missing?

For example: I only have a few songs that have the Album Artist tag - mostly for things like grouping "Fear of Pop" with "Ben Folds" - and for the ones that have it, I want them to be sorted that way. But if I tell Songbird to set up folders by Album Artist, it takes the vast majority of my library that DOESN'T have this tag, and dumps it all into an "Unknown Album Artist" folder. What I want to do instead is have Songbird look at the Artist tag instead if the Album Artist tag doesn't exist. I believe iTunes does this in its sorting, but I'm hoping to move away from iTunes entirely and just keep it around for AAC playback and the music store.