Animating using circle joints for arms- warping problem

I have just starting animating, and have set my chars up with circle joints for arms. However, if I want to stretch or shorten my arm using the transition tool during the animation, it also warps my circles using in the circle joints. The end result is that when I then bend my arms and legs the layers do not match as my circles are now ovals.

Anyone have an idea of stretching or shortening limbs using pegs, without warping the shape of my circles in my circle joints.

Thanks for your help!