Billing based on Position Payer (re-posted again)

Question

Hello,
Let me explain my doubt.
Our customer, the way of working, after creating sales order with documents flow, is modify de Payer at position level and later create again the Proforma billing, and the final billing.
This crash with the standard way of billing, for example:
Sales order A
Header payer: n1
10 Position payer: n1
20 Position payer: n3
30 Position payer: n1
Sales order B
Header payer: n2
10 Position payer: n2
20 Position payer: n3
30 Position payer: n2
Final billing by standard:
Billing number 1: against payer n1 (OK)
Billing number 2: against payer n2 (OK)
The problem is against payer n3, system generate 2 differents billing documents instead of one per the same payer.
Is it posible on VTFA- Billing based upon Order, item level 'Data VBRK/VBRP' , create a routine with a ZUKRI in order to billing by positions payers??
Another solution, on VOPA,delete PY for header billing partner procedure and add PY to position billing partner procedure?
I would be pleased if you can help us?
I have created this 9XX rutine and now system is splitting by WE instead of RG:
DATA: BEGIN OF ZUK,
MODUL(3) VALUE '902',
VBELN LIKE VBPA-VBELN,
POSNR LIKE VBPA-POSNR,
PARVW LIKE VBPA-PARVW,
END OF ZUK.
ZUK-VBELN = VBPA-VBELN.
ZUK-POSNR = VBPA-POSNR.
ZUK-PARVW = VBPA-PARVW.
VBRK-ZUKRI = ZUK.
Any idea
Thanks in advance

Answer 1

Hello,
I have created this new routine and now system is splitting by WE instead of RG:
DATA: BEGIN OF ZUK,
          MODUL(3) VALUE '902',
          VBELN LIKE VBPA-VBELN,
          POSNR LIKE VBPA-POSNR,
          PARVW LIKE VBPA-PARVW,
        END OF ZUK.
  ZUK-VBELN = VBPA-VBELN.
  ZUK-POSNR = VBPA-POSNR.
  ZUK-PARVW = VBPA-PARVW.
  VBRK-ZUKRI = ZUK.
Any idea?