Thanks everyone for the replies and tips!
Update:
I ended up using a dremel to make a cut on the inside housing and pried it apart until the square nut came out. After looking at the link that SugarBear posted I intend to take both housings off in favor of using carriage bolts.
I may also get a couple acorn nuts to see how they look if there is room to slide in the carriage bolt from the tire side and use the acorn as the finish on the grab rail side... This will also require the 10mm front rail bolt's co-operation. It seems like it might be a better finish then a boring hex head or cap. I like shiny things.

worthless without pictures as always, here is the damage:

