To setup reverse 2up tracking:
1. Login to admin account
2. Go to Manage Billing -> Edit Billing
3- Click Add a Pass up button to setup custom compensation plan
B would still receive the passup from C as long as his account hasn't been suspended, even though he has not yet given his 2nd passup to fully complete his 2-UP qualification. The next person that B personally refers would be passed up to A.
It will use the passup tree, but all existing members would be structured like regular and would look like regular (no one would have any passups). Then, moving forward as people signup it will try to force people to get their missing passups.