clothes pin clamps....it might be a better idea just to go to Home depot or Sears and get stronger clamps.....they are still pretty cheap and less likely to not have the tension that is needed. I have had a cam rotate pretty abrupty, and depending on the type of clothes hanger, it might not hold the cam sprocket in place. The ones I saw in Sears were only $1.99 a piece.
Another substitute that might already be in your tool box is to use vise grips to hold the two sprockets in place by clamping them together side to side. Just be careful with the amount of clamping force as I suppose you could damage cam journals if you clamped them real hard.