Boiling does work somewhat I've used it in trying to salvage 3 tires from rims. 2 tires came off fine (after fighting with them) 3rd one well got totaled its more hit or miss. Also be careful you don't burn your hands with the boiling method. Can I recommend the boiling method? not really its very time consuming (I spent around 40-50 mins a tire) and can be quite painful (hot water shot into the gloves I was using).
Personally like others have said if your not trying to save the tire just cut it off down to the rim ,and dremel the rest off the rim with a fine sanding bit. it will probably be the fastest, easiest, and safest way.
Later on I got to do the opposite I have a rim I don't care about (the hex hub stripped the rim) but the tires almost new. I'm probably gonna just cut the rim up and sand off the nylon
