The Rickson sweep has you lift the guy with the one hook, then extend your other leg and scissor it back against the guy's "free" leg from the outside-to-inside. It's basically a butterfly scissors sweep.
You can see the fight this clip came from here at about 40 seconds in.
The BJ butterfly sweep involves almost the exact same motion. The difference is that instead of using that outside-to-inside scissoring motion to attack the free leg and turn the guy over on his base, the BJ version has you switch your hips and, in the process, turn the guy over.
I broke it down into two different clips so that it might be a little easier to see. Again, the motion of your free leg is more or less the same: outside-to-inside.
The second clip comes from a B.J. Penn sparring session you can see here, with the sweep coming at about 20 seconds in.
I love the idea of having a solid butterfly guard because it can be used in both no gi and gi with little adjustment. It's also a nice, open or dynamic guard to use against "good posture" guys I can't break down from my closed guard. Adding these sweeps to the mix should be a priority when working the butterfly guard over the next few weeks.
