Partially applying Deposit to Invoice

Hi

I'm trying to partially apply a Deposit to and Invoice.

e.g. Deposit Amount = 10,000

       Invoice Amount = 2,000

Now, I only want to 1,200 from the Deposit to the Invoice, while the customer has to pay 800. This will reduce the Deposit Balance to 8,800 while there will still be Balance of 800 on the invoice.

The current functionality will apply the full 2,000 to the invoice. Is there a way, the above scenario can be implemented?

Thanks

Amar