How can we improve WHMCS?

We try to manage reseller as a client group by allowing them to pay all domains by site credit as a merged invoice at the end of each month.
It would be great to have more control over the invoice creation process, since we do not want to manage the individual invoices.

This feature would either allow the paid credit not to be marked as an invoice or an equivalent alternative.
Right now we have two invoices linked a domain, one from the credit recharge and one for the credit payment for that specific domain.