Splitting of invoice document into multiple line item when we using DP91

Dear Experts

We are planning use Resource Related billing process with Projects / WBS elements .In that process we have booked cost on WBS elements  by using different Cost Elements and When we performing DP91 system generating a multiple line items on Debit Memo request , but business expects to generate a single line item for the total amount

Could you please explain what are settings to be done to generate a single line item on debit memo request when we use dp91

Thanks & Regards

Gupta