how to handle product donations

Occasionally we donate products that we manufacture and I'm trying to come up with the right way to handle this.  If I do an inventory adjustment with a negative number I can't override the unit cost and half the time my unit costs come up as $0 (not to mention I'd like the donation amount to reflect what the product would retail for not the unit cost).  I thought it would be simple to do an inventory adjustment and apply it to our donation account but without overriding the unit cost it isn't correct.  Any help would be appreciated?  Or