A custom fabricated caliper bracket is all that's needed to add a larger diameter brake disc (along w/ a 6-pot caliper, if compelled). And, a different brake master cylinder if applicable (or re-do front/rear brake-bias?).
Question arises... why even do such? It'd presumably add noted unsprung-weight/rotational-mass for marginal (if-any) notable improvement in brake performance for the sake of cosmetics (filling out the space within the wheel spokes).
If anything, going w/ an OEM-sized after-market carbon-composite disc & applicable brake-pads from
MovIt could offer better braking, weight reduction (relative to the stock setup & optional McLaren carbon-composite setup), and preserve the "steel" brake discs for posterity's sake. Or, opting for larger after-market carbon-composite discs w/ applicable brake-pads for use w/ the existing calipers (again, requiring a custom caliper bracket) or pairing that w/ 6-pot calipers w/ the custom bracket, is a viable option w/
MovIt.