Well as you told me privately, you want this for Linux, and that means a kernel module. Perl is actually an abysmal choice for writing kernels in. They have all sorts of silly limits like staying within very little stack space.

However not all hope is lost. The idea you want does come up from time to time. Also it seems that there is something out there called userfs, which is a kernel interface to user level programs that implement a filesystem.

Seriously I would do a good search on this and see what you can turn up. I doubt that any great solutions exist, but you are far from alone in wanting this, and you should be able to scare up something.

And BTW, good luck. :-)

EDIT
FWIW my personal opinion on the question is that it is something a lot of people want. Just because a pure Perl solution would be a bad fit doesn't mean it isn't a good question to ask. Indeed if jettero does manage to track down and play around with userfs, I would love to see a Perl interface built. Perl may not be a good fit for a kernel, but it is great for building interesting prototypes...