withholding TAX

In existing system we have only option to calculate TDS on “Percentage on Gross amount” whereas “Percentage on Net amount” is not active and cannot activate with configuration (possible only with code change).

Now there is a law change in India that from 13th Jan 2014 onwards we need to calculate TDS on Basic value of Invoice, can you please find out that we can do this with code or we need to do through patch from Microsoft.