We found out a few days ago that George has a tiny bit of bumblefoot. I get to do a bit of surgery on her very soon to fix it. I'm really not looking forward to it, but it's for her own good.
I was able to get rid of a moderate case of bumblefoot without surgery with the solution in the link above. I also scrubbed the bottom of the foot with Chlorhexadine wash and soaked it in Iodine and epsome salts to reduce inflammation. I actually didn't soak it in the antibiotics until about 2-3 days in. I also put topical antibiotic ointment and then bandaged it with something like vet wrap. The swelling went away and later the scab fell right off. If you take care of it earlier and not let it get really infected you should have good luck with non invasive treatment.
Having dealt with the surgical approach to bumble foot this year, if I had it to do over again I would try the non-surgical remedies first. Once you have an open wound on the bottom of the foot you HAVE to wrap it to keep it protected. It's a royal pain getting the vet wrap on well. If you're also soaking the foot twice a day after the surgery then it's twice as big a pain.
I also read recently that just having a black spot is not bumblefoot thus there is nothing to cut out. I would definitely take the non-surgical route first. Also, if you have Vetericyn, give that a go.