I know there aren't many "roto-bars" out there anymore, but they allow you to turn your hands in a supinating action against resistance as you do the exercise.
The more weight you use, the greater the resistance as you turn your hands. If you were to do the exercise correctly the biceps would be doubly taxed, not only in the portion of flexion, but also in the action of supination.
I would also assume that maintaining as much thoracic and intra-abdominal pressure would help hold your spine in place, which in turn, would help keep you from cheating.
Everyone I see curling uses momentum to get the weight up. You'd be better off leaning against a wall and keeping your elbows stationary.
There is this one dude at my gym that is about 6 feet tall and about 150 lbs. soakin' wet. He cheat curls 135 lbs. regularly. I'm waiting for his back to break or for him to fall backwards when he tries to reverse-press the weight at the top of the rep. His joints are already turning to shit just because of the way he lets the weight drop. His elbows are probably like a worn out U-joint by now.
Another year (or less) and he won't even be able to whack off...