Plenty of people have splinted injuries like this. Usually just vet wrap is enough. You can get the same thing in the drug store for people, brightly colored wrinkly looking tape that sticks only to itself. Wrap it around several times. Watch the foot to be sure it is not too tight; take it off and rewrap it if the foot swells or the skin turns grey or blue.
It is a personal choice whether to kill the bird or try to heal it. Without an xray there is no way of knowing exactly what if anything is broken, and the previous poster is correct, there is a good chance it will not heal "normally" and the bird will always have a defect, but birds can and do live like this, with care, depending on how it comes out. One experienced chicken keeper on here has (or had, I don't know) a rooster who was seriously injured and could never walk again after he finally healed. She had a special home for him on her porch and would carry him to the others for social time every day, where he would lie on the grass. Lots of things are possible!
I am not a vet, and I am not saying vet care is not needed. Obviously, that would be the ideal route, it's just that many BYCers choose to decline that expense.
