USE of APO/FPO By Contractor for Contractor Performance

Does anyone know if we can allow a contractor to use the military postal system to ship repair parts overseas? The FAR and DFARS did not provide any guidance. I found the DOD Directive that governs the Military Postal System and it states that contractor employees that accompany the force are allowed priviliges at APOs but it is for their personal mail. I suppose this is how the contractor employess in Afghanistan are getting their mail back home. But what about a company getting repair parts?