Just came across these in browsing around for BRZ stuff yesterday. Turns out someone's already done what I was thinking of having made - custom aluminum wing risers using the factory 2017+ wing holes and 3D-scanned from OEM mounts to fit a SARD LSR-style wing. The SARD-style wing option has adjustability to change the angle of attack on the wing, and they also went about making it a modular design that can mount the OEM 2017+ wing!
Here are a couple of pics:
With the SARD LSR style wing:
With the 2017+ OEM wing:
Check them out at Battle Garage Racing Services! Here are the links:
For the SARD-style wing kit
and
For the OEM wing kit
They say:
"Only interior-side drilling required, maintaining the sleek exterior of your trunk. Light modification to factory holes is required." and that interior-side drilling is for
"Steel support plate designed to be bolted to inner structure of trunk to further increase support for added downforce of a carbon wing."
They're certainly not cheap, but these are DEFINITELY on my list now once I have funds.
I'll probably buy the riser kit for the OEM wing first, and then decide if I'll also opt for the SARD-style wing down the road. If I do, I'll buy the full "carbon wing upgrade kit" they list to get both the wing and the adapters, and then I can swap back and forth between the two for road vs. track use.