One possibility is to be the seventh son of a [seventh son][1]. 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.

The wikipedia article on [werewolves][2] 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


  [1]: http://en.wikipedia.org/wiki/Seventh_son_of_a_seventh_son
  [2]: http://en.wikipedia.org/wiki/Werewolf#Becoming_a_werewolf