Prototypes in folders?

Is there a way to organize prototypes so they’re in some kind of folder structure? Right now, the VASL module has several dozen prototypes that are all together in the same level of the prototype section of the buildfile - makes it painful to navigate through and see what’s going on.

I’m not asking for the folder structure to imply some kind of inheritance of Traits, although that might not necessarily be a bad thing. But even just enabling prototypes to live in folders would be a Good Thing, IMO.