If the fish is almost ceartantly doomed it worth a try. This seems bacterial not viral so it should respond to the correct med. Without a lab test I can't know if it is gram-negative or positive so a good start would be a broad spectrum antibiotic like minocycline. Most fish infections are gram negative tetracyclines are mostly gram positive, minocycline is a member of the tetracycline family with a broader spectrum of coverage. It is possibile this bacteria is gram positive and standard treatments would not help. As another option It would be interesting to see if Neomycin would work since you said a general antibiotic ointment seemed to help. Neo is available on bouth topical and oral, Seachen sells noeplex that could be disolved as a food soak and fed as well as be used directly in the tank. I think both suggestions are viable options and should be considered by the OP.
It would be interesting to know what other hobbiest have tried before and what level of sucess if any was achived.