I would go for any kind of slope reading tool in the designer.
Being able to move the cursor around and see the slopes in different parts of the green would be handy as well (instead of moving the flag around to get that done.)
While you're at it adding some sort of measuring tool would be a bonus. However, instead of displaying just a distance displaying elevation changes would be a nice touch as well.
It would also be nice to have some way to execute a certain type of shot in the course designer. I waste soooo much time repeating approach shots when my darn controller hits the random 85% shot or I fail to hit it straight after playing over and over. Now, I usually let it go to see where it lands but when I want to see where the ball winds up when good players hit it I'm forced to waste a bunch of time hitting again and again.