How can I exclude backorders from Credit Level Checking?

We have a scenario where we would like to reduce what we include in customer's Open Order Total $, as we have too many orders on backorder and this is causing many orders to go on credit limit hold. We also have a long allocation window (28-36 days) which was done to increase inventory availability, however the negative consequence of that is our open order total is high, which creates a problem for credit dept.

We would like to limit the open order total to only orders that we are actually able to ship within the next x days (exclude backorders and those with Sch Pick Date > certain number of days).