That sounds doable. (After I posted my original scheme, it occurred to me that the only way it could work would be if you could also implement some kind of system that would slow time itself down!)
So do you have any ideas about how this could be done simply in hardware? I know this would be best handled by a microprocessor and software, but I'm curious to see if some simple and elegant hardware solution could be cooked up.
Also, while we're at it, let me add something else to my wish list: the problem with your suggestion is that it would result in an extremely narrow band of frequencies (in fact, only one frequency). Let's say I wanted to allow a band of frequencies through, like 0.1 - 2 Hz; how would I sample for this? I guess you could run several parallel sampling operations at different frequencies, but wouldn't that result in a very "spiky" result? Ideally, I'd like a fairly "smooth" response plot within whatever passband I select.