Not sure if there's enough room, but the new Rasertech AC motor is about the same size as the Prius motor, so it might be able to slot in. It has a reasonable output too... is
500 bhp enough for you!?
http://www.rasertech.com/monaco.html
Being sensible, however, you'd need a heck of a battery to be able to give it that much juice for any length of time (sorry, stock battery won't be up to it!) You'd also likely melt a fair number of tyres (not to mention transmissions, driveshafts etc) but it would be cool to see a 500hp electric Insight beating all-comers! 700 bhp per tonne would be
waaayyy more than a Ferrari Enzo or even a McLaren F1!