Rescue Goldie with swim bladder issue

Well, I hate to tell you this Scully, but this is exactly why it's so important to plan before purchasing goldfish. Although you have a backup plan for the little fancy, ultimately he probably won't do well in a pond. If he's alone, he's at risk of being dinner for predators, and if there are other fish, he'll won't be able to compete for food. Beyond that, you brought home a sick fish, which is never a good idea. I commend you on the rescue, but you may end up spending a lot more money and effort on bringing him back than you wanted to.
That aside, we'll do all we can to help you get the poor little dude healthy again.
Your plan to feed him shelled peas is good, but since he was so cramped at the store, I would skip the fasting and feed him only peas continuously for a week. He's likely already been fasting for a while!
That should clear out his system and help purge him of any swallowed air. Be sure you cook the peas so he's not gulping at them on the surface.
If he doesn't improve after that, then we're looking at a much more serious problem. Surgery can correct swimbladder problems, and if there's a university nearby with a veterinary program, you could be in luck. You can try contacting the program director and ask if there are any students specializing in fish medicine that would be interested in operating on your fish. Sometimes they are willing to do the surgery at no or low cost.
The only other option would be to construct a harness for him, but in a pond that's definitely not a viable option.
Finally, you're looking at euthanasia if none of these are successful.

Best of luck, though, and keep us updated on how he does.