How can we use more than one return address for different packages?

I've agreed to do order fulfillment for a friend's company. But we need to have a different return address on their shipments than on ours. The only way I can see to do that now is to pack and print labels for all the orders for one company and then go in and change to a different return address and do all the orders for the other company. I thought upgrading to a plan with multiple users would let us have multiple return addresses, but now I'm not certain. Is there a way to do this, so the return address is keyed to the user and not to the account?