ok, I've tried this and it gets the settings showing in usergroup manger. You
must install the product on page 27 for this to work, then replace your bitfield_userpage.xml with the one attached here and then rebuild bitfields. It will then appear at the bottom of the usergroup and make it 3.5.1 compliant.
EDIT: I've attached the product again to save people from having to look for it credit for the product goes to cclaerhout
EDIT 2: Working in 3.5.1
clicky