Lot Expiration vs. Best By Date functionality

Hello,

We are using lot control to manage items from our vendors that have a shelf life/best by date/expiration date.  Since we are a distributor we have set our Best Before days to be 6 months prior to the Expiration Date that is created by the Shelf Life Days setting.  This works great for managing what we ship to our customers but it does not work well for managing internally since the items show available through the expiration date even though they cannot be shipped 6 months prior.  Also MRP recognizes the expiration but not our internal Best By.  Is there