VAT Calculation:Base amount after WHT deduction

Hi SAPers,

We have a requirement in azerbaijan that VAT calculation is based on the Base amount after WHT deduction as below where both VAT and WHT are applicable within the same Vendor invoice.

Net amount in Purchase Order (Cost) 1100.00 AZN

WHT (Amount to Vendor x 10%) 100.00 AZN (1000.00 X 10%)

Amount to Vendor after deduction 1000.00AZN

VAT (Amount to vendor after deduction x18%) 180.00 AZN (1000 x 18%)

So I am faced with the problem about the base amount for VAT being after WHT deduction.

Could any of you shed some light on how to resolve this problem to get the Tax baseamount with WHT deduction?

Thanks in advance

Taro