Actually, I didn't need this after all.  I'm using Automaton from the arrows package for the first part of my pipeline.  Only the zlib compression step is a Conduit, so I can just use arrow functions to lift Flush to the rest.

Nonetheless, someone else might want to do this.  Now that I think of it, not all of the arrow operations make sense (in particular, (***)), but splitting data between conduits (like ArrowChoice (+++)) does make sense, I think.