We would like to use the Internal Billing functionality of Projects for an Intra-Operating Unit scen

We would like to use the Internal Billing functionality of Projects for an Intra-Operating Unit scenario but do not want the Invoice sent to A/R to increas the balance on the Internal Customer. And likewise the A/P Invoice that is created by the A/R invoice not to increase the payable. Has anyone come up with a creative work-around to this scenario? My first thoughts were to create a new A/R Transaction Type with the Open Balance option disabled but Projects does not like this. Any ideas would be greatly appreciated!