wfairley -
This one has been in the R&D stage for *years*, so it may just be vaporware :
Electrocharger / Retrofit PHEV Hybrid Conversion Kit :: Sigma Automotive
electrocharger
Directory:Electrocharger - PESWiki
In a previous iteration, it looked like it would retrofit down to compact cars. However, now I think it's only intended use is for larger RWD vehicles, aka big trucks.
CarloSW2