Yeah - Ok I got it now...
I thinks the challenge; "... lies not in our stars, but in our "cars"..." Sorry Shakespeare
The car presents itself as an analog of a wing. So getting a high pressure over the top of the car would take some real doing. Consider the following comparison:
A vert may have more potential downforce over the center of the body - due to turbulent flow -- maybe not.
Hopefully the image shows how the shape acts like a wing and creates low pressure on the upper surface -- just like a wing.
The question might be changed from; "How do I create higher pressure on the top of the car", to; "How do I get lower pressure underneath?" It is really about the differential in pressure.
The underbody offers many "unseen" opportunities to create a low pressure area(s) and place it where you want - center of the body. You'll give up some ride height - maybe - but it would be unobtrusive and should be consistent throughout a speed range. That is to say - no pitching moments as you accelerate/slow down.
Your Pace Car style front spoiler should offer some help in the corners you mention. Additional drag through "Active Aero" would also play well for braking - but not all racing associations permit these.
Hope that info is useful.
Cheers - Jim