It's best to speak with your vet. He/she might be able to inject the splints to reduce the swelling and the bone remodeling.
How old are the splints? If they are too old, the bone might already have too much remodeling to be able to reduce the splints to any extent without surgery to remove the splint or a portion of it.
As far as the painting something on that burns, it's called a blister--there are several different types, but they can be painful (sometimes pretty effective, though).
Again, it's best to talk to your vet before doing anything. Usually splints will only be painful for a short time, but after that they don't cause much trouble -- just ugly.
Also, you might want to investigate what caused them -- trauma, poor hoof balance, poor comformation, etc.