Nice idea - but if you're looking for a reliable and relatively trouble free way of making the commute easier then I can recommend electric as the way forward. A colleague at work has spent the last few years refining the art of making electric folding bikes. We all take the mickey out of him for his laziness but in reality it means he cycles to work a lot more often and in all weather conditions because he knows that it'll not be too difficult.
He imports the motors and batteries from China and builds his own wheels with the motor in the front wheel. There's no legislation to get around except that you're limited to a maximum or 15mph when on the motor alone.
If you're interested to know more I can put you in touch with him as he'll talk about electric bikes until you have to ask him to stop...
I am quite interested in talking to your friend, electric motors seem like a cool option as well. I found this website http://www.dvice.com/2013-7-23/removabl ... -instantly
that shows a device soon-to-be available that would be right up my street I think. It seems identical in idea to the Trojan mini motor of the 50s except it uses electricity rather than petrol. Though it looks quite pricey at $1190 which is £741.43 hmm. Yes put me in touch with your friend, I could talk to him about different options