At this point...the first thing that comes to my mind is heat.
If you have a torch, some tools (pliers to pull something hot), and possibly a lift to get you some room to maneuver (without catching anything on fire or melting any trim pieces)...you should be able to get it off.
If not, your local muffler shop might do you a favor for $20-$30 to get it off for you...and possibly install the replacement tip. All they can say is yes or no, and multiple local shops are only a phone call away.
