Define Fourmulas For Calculating Withholding Tax

Dear All
 
When to "Define Fourmulas For Calculating Withholding Tax" we can define slabs for withholding tax calculation with different % rate according to the increasing base amount.
 
But we require to add a particular amount with increasing rate like
 
5% withholding tax upto Rs. 400,000/-
Rs. 12,500 + 10%  of the amount exceeding Rs. 400,000/-
Rs. 72,500 + 15% of the amount exceeding Rs. 1,000,000/-
 
Does any one knows the option to add a fixed amount with %.
 
Regards