It turns out it is *really* hard to clamp binding in a reinforced F-hole. You can't really get any clamps in there and using binding tape is equally problematic. So, the only solution was to make some custom clamps. It was still going to be tough to get the binding in place, glue it, adjust the position and get it clamped before the glue started to set, so I rehearsed it and numbered the order to apply the clamps.
Once it was set, I put a block into the cavity and used a nice sharp chisel to trim the ends at the required angle, simple join but that would be enough for me.