Do you anticipate they will go into the game with only two backs on the bench or will they be looking to bring someone in from the JID?
The big question would be who from the JID? Would a safer option be to bring in a winger?
I know its a left field option, but throwing a bit of caution to the wind (and I think we need to), Christian to 10, Taliauli to 12 (he is ex league and 7's so may be a surprise at 12), and the Doyle to 13 (yes, the nutty one - he can defend, run a ball up and has some speed...and a viable option).
I would then also consider either Smiler (has played 7s) or Butler for the back up 13, leaving option for Robbie to play 10/12/15. Christian to play 10/12/15, and Ah-Wong to play 12 or 15 or even Joe at 15 if needed. Henry can go back on the wing to keep the opposition worried about our width and maybe in tandem with Joe draw the pressure off the centres.
Edit - after all that I missed out Iona!