Requires a dinner booking via Dimmi (aka The Fork).
Available in Sydney, Brisbane or Melbourne.
Make a booking at one of the restaurants and on your restaurant confirmation email will be a link with a unique promo code embedded. I was able to book at a car park not listed as a "best park" on the promo web page. I then cancelled the dinner booking, obligation free. Or you could keep it for 50% off dinner as well.
I made sure my dinner and parking booking were in the same city and on the same date, not sure if that's required.
I ended up with $6 booking, could've been $5.50 if I was willing to walk further. $1 booking fee applies after discount.
Great hack, will remember this