So I was talking with a friend who knows a lot more then me, and this is what we came up with.
I did some research on the way the skates work in the anime/manga, and it seems the out of of the motor is based on the rider. (stronger kick=more output). So I got to thinking. Why don't we start with augmenting the skates? I think we could use a friction motor, like the one's in toy cars. It uses a flywheel. They do a great job of keeping a constant speed, and the harder the kick the more you will get from the motor.
I feel this is extremely practical. The motor is able to be made that small (they use them in toy cars) and it solves a power problem. Friction motors in the front wheel of each skate will allow the rider to not only get to higher speeds but maintain those speeds for some time.
Let me know what you think. If I find extra time I'll see if I can draw of some rough plans.