Hmm, not sure Cap. Mine doesn't have one nor does it have a screw hole as in your picture. I think the HiAce and LiteAce models just folded the passenger and middle seats right back so that they didn't need a hook. Though I'm not sure as mine came with the divider bars which stop the seats going right back. I just seem to remember helping a mate with his LiteAce and the seats folding right back near 180 degrees.
I'm in Australia actually, although Tasmania (my state) is probably more like what you think of when you think NZ than AUS.
I will definitely keep your idea in mind.
Cheers - Doc