I use a cross trainer, that is basically a bike where you stand and move your arms as well. I do however use it on high resistance (too lazy to stay on it for too long
I noticed that my spasicity in my legs was partially caused by a weakness where my knees would not lock, straight. So I have been strengthening these by jumping on the spot. It appears to have helped.
Dont worry, I havent missed the point that the cycling should be NO RESISTANCE. I have been meaning to get a stick to enable me to do no resistance training of motion, to also teach my legs to do a full circle pattern, instead of the short stroke of my X-trainer (or even a bike). Imagine cycling in the air with your feet forced to stay 50cm apart (vertical plane) all the time.
I do notice after getting off my X-trainer, the spacicity seems less, but I am dead beat.