Just give it
runSurfaceAngle = 0;
jumpSurfaceAngle = 0;
runforce = (some lower number than 9000 (before you comment, 9000 IS the default runforce) here)
This way you'll need some speed to get up hills, and there will be noticeable acceleration times and sliding.
As for the "this can't work as a playertype" crap, it would be best if this WASN'T a vehicle. It's a sphere, it doesn't need to actually roll. It's going to look the same most of the time anyways. The last thing you need is going through walls.