Negative Payment Recording

Negative Payment Recording

Hi,

I have client Payments such as a single payment contains payment for one invoice and also TDS deductions from multiple invoices. In such a case negative Payment value is required. How do I do It.
Example:
Payment Received: 13111
To be mapped against the following:
inv 115 tds   - 2000
inv 116 tds -   2000
inv 117 Payment - 17111
Explanation:
17111-2000-2000 =13111
How to do this. This can be rectified if the system allows negative Payment value. But the system does not allow. How to enable it.