program income

I am looking for help on how people deal with "program income" on Grants. I see how you can you identify the expected program income on the Proposal but this seems merely informational. Assuming that accounting method for program income is the "additive" method (e.g. you get to spend the program income on eligible grant expenditures), does this mean that you need a mechanism to account for expenditures that will be funded by the program income and prevent them from being billed against the Grant contract? Perhaps this can be done with a unique Activity or you might trap for