Halfback and crossing into pocket

[RobLev]

[LAWS]20.3 (f) Binding by all other players. All players in a scrum, other than front-row players, must bind on a lock’s body with at least one arm prior to the scrum engagement. The locks must bind with the props in front of them. No other player other than a prop may hold an opponent.[/LAWS]

I realise that your question is rhetorical, but the bold+italic highlighted above are sufficient for me.

If that prevents flankers binding in the thrid row, it also prevents the #8 doing so. I repeat - there's no special exemption for the #8 from the Law - they are "all other players" just as much as flankers.