Years ago I bent the bow rail stanchion on the port side, about mid-way. Called a local welder who brought out a mobile welder and some strong-stock replacement (much better than the OEM). Cut it to size and angle to match the bent one. Couldn't get access to the 4 nuts. He cut the stanchion at the rail and then drilled out the heads of the 4 bolts on the base. The bolts just dropped inside. Then he cut the base from the bent stanchion and welded it to the new stanchion. Epoxied the base and screwed over-sized screws into 3 of the bolt holes. Could only access 3 of them. Then welded the new stanchion on to the bow rail. Results are a stronger stanchion/bow rail and very secure at the base. This guy was good. If all fails on gaining access, perhaps drill out the 4 bolt heads. Then lift up the base and epoxy, screw-in the base.
One pic show what the bolt and washer looks like for one of the cut bolts. I found it by chance while trouble shooting a problem with the fwd sump-pump flow.