We too ave graduated to an extremely large dildoe with similar results. I usually describe it as being the size of a small baseball bat. It's a bitch to get in sometimes but the results are worth it.

I also just recieved a set of clover clamps in the mail which I am saving for this weekend.

http://www.aswgt.com/cloverclamps.html

I understand they tighten as you pull on the chain. I'm dreaming up a scanario wherein the chain from the clamps is attached to her spreader by a very short length of rope or chain. As her legs tire and start to drop, the clamps will tighten and stretch the nipples. Ill have to let ya know how it works out!