Adding 2nd Facebook account?

No, and you can't have the same app twice either. Best workaround would probably be to use one account in your browser.
 
alternately set up a second user on the Nexus 7 and then they can acess Facebook under that account
 
alternately set up a second user on the Nexus 7 and then they can acess Facebook under that account
This. If you don't want to be switching between profiles then you'll need a browser open with one account and signed in with the App on another account. I'm not sure that there is another way to manage multiple Facebook profiles on mobile.
 
Thank you all for your help. I had thought of both those options, but was hoping I'd missed something. ;-)