Is there a way to prevent uke from rolling out of a shihonage pin? How did shihonage become a pinning technique anyway? Maybe it isn't meant to be a pinning technique?
One method I have used in the past is when you finish executing shiho nage and you have your left knee up and your right knee down (I am looking at this from a Yoshinkan approach) I will spin on my right knee dropping my left knee to his face. I will put my left knee into ukes face/throat while maintaining that shiho nage lock. I will then torque on ukes wrist pulling it to my center. This usually stops them from wiggling out of shiho nage.