Adapting existing vehicles for plug-in hybrid capability

Hi,
I am very curious whether any research has been done into retrofitting plug-in hybrid capability into existing vehicles, perhaps (I'm at not a mechanic!!) by creating an alternate back axle etc.

I know this might sound wacky but we have great hydro and windfarm potential, and if oil rises rapdly, it will still take years before electric vehicles can become widespread, particularly as we are competing for supply in a world market as a minnow. Can a bit on No 8 wire genius find ways of retrofitting, say the 10 most popular small car makes, 5 years old???

Just a thought - Dave