So basically, I think this exchange could be used in such an idea. It'd have to tie in with an accounting information system, and other systems. Possibly an ERP. Management can approve of all intracoin/fiat trades on the exchange, because it means a department will need to make an external purchase, and management may want to approve of it... to see and approve where its real money is about to go. Also, a conglomerate of companies tied into 1 exchange and 1 intracoin would be interesting.
add: company exchange can also hold bitcoins/??coins for spending at other companies that accept cryptocoins. And sales can be received in cryptocoins. If that was the case all the time, fiat would only be needed to pay government taxes.