Equipment Rental Charges

I have created a Time and Materials project that I am using to charge employee labor and materials related to the project. This is for a field service type of activity. For these types of projects, we also charge the customer a daily (or weekly) fee for equipment rental. Since we have purchased the equipment outright - for example a truck - and have it listed as a capital expense, I don’t want the project to absorb any cost for this rental - I just want to be able to charge the customer. Normally I would just create a miscellaneous charge on the invoice to cover this rental cost. However, I am trying to use the ‘Project Invoice Preparation’ action in Project Entry, and the ‘Time and Materials Invoice Review’ screen to approve the invoice. When I approve the invoice so that I can be retrieved in AR Invoice Entry, the invoice comes into Invoice Entry complete and cannot be edited or added to (unless someone can show me how to edit it). What I would like to do is create some sort of ‘expense’ or ‘purchase’ (not sure either of those is the right word) that I can add to the project that produces zero cost to the project but provides a ‘sale price’ that will show up on the invoice to the customer. Is this even possible?