Someone on Lego Universe showed me an easy way to beat them in the Battle of Nimbus Station.

First, you get out a wand of some sort (preferably a Mosaic Wand) and lead the Riders over to a long bush on the edge of the battlefield. Then, you start repeatedly using your wand attack, which goes through the bush, on them. They can't attack you because the bush blocks the projectiles. And viola!, you have four defeated Riders.