In one of those cases where you ask a question, don't get an answer, then spend far longer than you intended playing with the problem, I've just added a Pipe mechanism to Fussy (why to fussy, you ask? Well because that's where I wanted to use it). Basically it provides a small wrapper around subprocess that lets you easily setup chains of subprocesses, files, generators, etc and have them iterate reading/writing until they are all closed.
You can read samples in the documentation. It's still pretty rough, and there's lots of things still to be worked out, but oh well, it seems like a fun interface sketch for now.