I'm not sure if you're looking for a motorized way to rotate it.. if so, I'm not sure what the best mounting solution would be.
I have a 19" LCD in my mini upright and I rotate it manually (takes 30 seconds).
I used two mounting shelves for the monitor.. the higher one is removable and it's for the horizontal orientation. Below that shelf, there's another shelf for the vertical orientation. If this sounds like it would work for you, I can post pictures if you'd like.