Can't get nut off LCA pivot shaft w/ poly bushing (shaft spins)

I've tried with an air ratched on and off the ground, no luck. My impact will not fit in the slot. I'd like to avoid taking the control arm off the shaft since I have just recently installed the new bushings and shells and would like to avoid that pain in the ***. What do you guys thing of somehow notching the exposed threads of the shaft in a way that I can get one wrench on the but and one open ended wrench on the shaft to hold it in place? And I'll see if I can fit a vise-grip between the LCA and the k-member in the morning.