AME approvals issues for requisitions

We are trying to find a way to build a rule for requisition approvals that can handle the scenario below

1) User A enters a requisition for $500 against CC 12345, they have the approval limit

2) there is an AME rule for cc 12345 that grants user B approvals under a different rule

3) User A & B only share approval limits over this one CC 12345 they have approvals over many other cost centres

4) when user A enters the requisition it must go to user B and User A for approval even though User A has the limits.