I agree the up and down run on the pedals is not good form. Feeling the seat between your legs, tilt at the hip a bit...use the same form you would use if you were to do a slight higher cadence on a standing climb (think Lance standing up on the hills).

Even when you watch the standing on Spinervals, most of the riders will take on the proper road form, they don't spin like a hamster, they create a smooth cadence...and if you need to add more resistance, add more. The add'l resistance helps teach you to create a smooth spin without stomping...and this is harder to do on your bike on a trainer than it is on a stationary bike. (I find you can get sloppy on a spinner bike without noticing you are stomping.)