Calculating withholding tax R04580 .

Hello to all,
Can we calculate withholding tax R04580 from the Taxable Amount and not from the Gross Amount as my client want to deduct the withholding tax before calculating VAT while system uses Gross Amount (Taxable Amount + Tax amount) for the calculation?
Thanks

Dear All,
I wonder if any can think of a work around solution for below case if there is no a standard one.

Thanks

[ QUOTE ]
Hello to all,
Can we calculate withholding tax R04580 from the Taxable Amount and not from the Gross Amount as my client want to deduct the withholding tax before calculating VAT while system uses Gross Amount (Taxable Amount + Tax amount) for the calculation?
Thanks

[/ QUOTE ]