How to set down payment amount to draw equal to the invoice total

Hi,

I am using DI server to create a partial a/r invoice document for a sales order for which one complete down payment invoice is already added. I am linking the down payment with this invoice document, but the problem is that the full down payment amount is automatically drawn with this invoice. I would like to draw an amount equal to the doc total of the a/r invoice I am adding, and the only way to get that total is after adding the a/r invoice document. But since the down payment can only be linked when the invoice document gets generated, this will not work. Please suggest how it can be done.

Regards,

Victor Mukherjee