This is how I do it:

def chown(self,user=''):
 user=self.acl_users.getUserById(user)
 self.changeOwnership(user=user,recursive=1)
 return 'Done'

put this in as an external method and call it on the object in question (either singular or a collection).

http://myserver/index_html/chown?user=philh

for example.