Thanks for all the responses, as I suspected people have managed to come up with quite a few things I haven't thought of.

In my case, I eneded up doing something much less cool, but more functional - since I only need the hash for read-only access, I just "flatten" the hash-of-hashes-of-hashes... into a simple hash with strings I wanted ('a.b.c.d') as the keys when I load it, and go from there - not as fun, but quicker.

Thanks, again.