With lower side doors and full windshield, my 900 got downright toasty in the drivers seat. Great for winter riding. At times way to warm on milder days. I removed my side doors and windshield for upcoming warm months and did notice that I was far more comfortable riding on a 45*f day a couple days ago. But another 45-60 days and it can be unbearable hot and humid here in NH, so looking for ways to keep radiator heated air pushed by the fan out of the drivers compartment will be on my list as well.
I haven't looked close enough to see how much space there is around the steering shaft to allow air to pass. But if there is room, it maybe as simple as fabing a frame out of aluminum and using that to sandwich a piece of rubber(old inner tube or like) with a hole in the middle and a slit to allow it to wrap around the steering shaft. Rivet the frame to the firewall . I built something similar in my old stock car and it worked well to keep engine heat out of the car.