Dustoxin

http://www.ehow.com/how_4618882_build-motorized-rollerblades.html maybe this?

but wouldn't you need to generate more power then your putting out? although it could prolong the energy from being depleted as quickly, but battery life seems to be getting bigger and bigger all the time, so maybe it'll be more practical, but until then keep trying. my friend and I will be tinkering around trying to get things to work, will take a long time.