Discounts in RQ

I'm looking for work arounds for the inability to take a discount on a requisition. It's possible in PO by using an Allowance type Add On Cost. However, our departments are working on pretty strict budgets using commitments and encumbrances and since we can't take the discount until it's on a PO, the budget is being hit by commitments that are overstated. I can't ask the requesters to calculate the discount on each line as that is too cimbersome.