Update, so I disconnected the hose at the accumulator and took the top of the compressor off, removing the attached hose from the vehicle. Then attacked the bolt with a dremel until the hose came free. Thankfully I didn't have to drill the bolt out, with the bolt head and hose removed, the remaining bolt now came out by hand!
Put it back together with new O-rings and took it off to be gased today, so far no leaks
Just in time for the first heatwave of the summer