One possibility is to be the seventh son of a seventh son. This is listed on wikipedia as a superstition in the UK. In Paraguay, Argentina and Uruguay, it is only required to be a seventh son. I recall this legend from childhood when I used to read books about the supernatural'supernatural.
The wikipedia article on werewolves has a section on becoming a werewolf. Some that you did not already list include:
- removal of clothing and putting on a belt made of wolfskin
- drinking rainwater out of the footprint of the animal in question
- rubbing the body with a magic salve
- draining a cup of specially prepared beer and repeating a set formula