No rules? I'd use a big elevated wing set for slight to no downforce on the straights and increasing downforce as brakes are applied, ultimately being a complete air brake if really hard on the brakes. Mercedes had an airbrake racer back in the day. And I dimly recall seeing a video sometime in the last few years about a supercar with left and right "ailerons" that in addition to downforce and braking, were individually activated for cornering assistance.
P.S. This isn't what I remembered but it's one example:
https://www.thedrive.com/tech/22150/...going-aircraft