Minimum Values in Billing Doc - Consolidated Invoice - How to exclude items

I have a requirement to apply a minimum charge to an invoice but the minimum amount is not to be based on the total value of the invoice.

The invoice is used to bill a rental contract via a billing plan, via deliveries based on actual usage and other manually entered transactions. All these contribute to the minimum value.

The invoice is also used to bill other debit notes during the period but their value MUST not be included when the minimum value is to be determined.

The minimum pricing condition is working as standard SAP, BUT I need to exclude the value of some of the line item. I can distinguish which item are to be excluded by the preceding document type.

Anyone has any idea of how to do this?

Regards