[kh99]

I haven't tested it, but I think this will work: create a plugin using hook pmdata_postsave_recipient and this code:

if (THIS_SCRIPT == 'register' AND ($user['options'] & $this->registry->bf_misc_useroptions['emailonpm']))
{
   $user['options'] -= $this->registry->bf_misc_useroptions['emailonpm'];
}