Thanks for all the responses. I did end up getting it off. Used a pair of needle nose vise grips to hold the bolt from spinning and then used a pair of snap ring pliers to remove the split nut. As it turns out the little plastic haunch on the inside of the insulator was broke off which let the bolt spin when trying to undo the split nut. I went and bought the replacement insulator from Steiner on my lunch break.
