The universe as an engine

Serendipity brought the non-zero vacuum energy and thermodynamics into my head recently, which led to a science fictional idea.

Engines work because energy flows "downhill". You can't do work with the vacuum energy because it has nowhere to go. Now if one could connect to a universe with a different vacuum energy, one could presumably do work. One might even bring universes of differing vacuum energies into being simply for this purpose. And thus the science fiction story -- the vacuum energy of our universe is rising because an entity is pouring energy into it from another universe ...

There's got to be a short story in there somewhere.