Ability to invoice a single line item

Every now and again we'll do a special project for a client and they want a separate invoice for it. Obviously we raise this in Sage but we need to be able to record the hours / activity etc in Mintsoft against a specific day(s) so it's logged in KPI's / margin calculations etc. Can we have the ability to select one line for invoicing?

Thinking further, we may at some point have a client who wants us to bill weekly for pick and pack but monthly for storage. As we record storage charges daily (as on numerous occasions we will see stock come in and out again pretty rapidly and it's either lost revenue if we take the snapshot for lower stock or unfair to clients to charge full capacity for the whole month) it'd be great to be able to say invoice pick pack and additional invoice items on x date but storage at a later date.