I'm sorry that I missed this post the first time around. (My excuse is that I wasn't here...)

For anyone else who runs across this post, the idea actually came up on the p5p list a couple of years ago. Ilya suggested that it would not happen any time soon, but suggested getting the same effect with a convoluted internal code expression. I reposted a variation of Ilya's suggestion at Re: Regexes on Streams, and tsee did the hard work of implementing it at Regexes on Streams - Revisited!.

Yes, it is horrible, ugly, and fragile. But it is here, it works (for most cases), and it is on CPAN as File::Stream.