BMW has been working on a combined ICE/steam engine recently. The first heat engine to achieve 50% efficiency was the Napier Nomad turbocompound
Napier Nomad - Wikipedia, the free encyclopedia
I think a great way to use exhaust heat is for an absorbtion cooling unit to replace the AC compressor. With a bit of redesign to the manifolds, solid-state junctions, as used in heating/cooling portable food service accessories might give enough to replace the generator.