Andre, Shen, Andrew, Jonpall and anyone else
I have been doing something similar but never passing fully to side control. I usually stuff the elevator/butterfly hook and end up trapping that leg with both of my legs and then work the pass from there.
What other details do you guy see here to make this pass successful? I have tried this during sparring and hit it 50% of the time. I noticed that you have to keep your hips parallel to the floor because if it starts to tilt towards the direction you are being swept you will probably get swept. I also found my success rate to be higher in no gi than in gi.
Perhaps the key principle that this guard pass is demonstrating is the old wrestling trick of dropping one's hip on the opposite side of where one is being swept. If someone is trying to butterfly sweep you to your left, drop your right hip (and raise your left hip) and that will make it harder for your opponent to sweep you.
Another thing: Once you have made contact with your hip to his hip, you have to keep that contact until you can get a good grip on his head somehow and finish the pass. Basically, don't release "hip control" before you've got "upper body control". Otherwise, your opponent is likely to regain guard if he's any good.
My 5 cents.
JP thanks for your 5 cents :) Took your advice and helped a lot.
My only other problem now is if the sweeper controls my arm by the tricep instead of the wrist, it makes it very hard to base out and do this move.