Row Security and Inter Company transactions

We have row security setup so that users can only update their own company's data. But we want to do inter company transactions and for that we do want users to update the other company's data. What is the easiest way to set up security so that only for inter company transactions users can update the other company's data but for all other transactions they can only update their own company's data? By Inter company transactions I mean mostly Transfer Orders (ST-OT).

We are on Enterprise One 8.12.

Thanks,

Matt