Is it possible to exclude the amount already paid and to show the full due amount in the invoices? Some clients ask to receive this kind of invoices
if you are asking about the due on the particular invoice, in custom theme exclude the heading Amount credited in totals field.
if you are asking the total outstanding due of a customer, you can expect this from @lubos in some future updates. i had already discussed regarding this few months back.
Your question is not clear. Are you saying your customers want additional copies of partially paid invoices that do not show amounts credited? If so, why? If they want to know the status of their account with you, why not send a customer statement?