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 ...