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.