Creating a Project Expense without affecting the books

We are a small custom construction company and we use the Project function to track project level financials. In projects we will see customer payments, related Bills (for special order materials, services & rentals), and Time Activities for labor spent on that job. The bills & time activities help our project managers know the amount of costs involved with the project so far. There is a third cost type, which would be materials used from Inventory. While we don't track inventory through QuickBooks, we would like the 'Charge' the project for the use of those materials we keep on hand. For example, if 100 linear feet of aluminum tubing is used, lets say it's $1 per foot, we'd like to see an expense on that project for $100 but not have that affect our overall company level books because from an accounting perspective, we've already bought and paid for that $100 worth of aluminum. Please let me know your ideas of how to best accomplish this. Thanks!