It isn't easy, but then its not terribly difficult either. The parts can cost anywhere from 600 to 800 depending where you get them. Keep an eye on the forum for folks with a VRSCD Nightrod, which came with mids. You can swap straight up. I bought my forwards and sold my mids to offset the cost.
Personally I love the mids on my D. They allow you to really get more out of the bikes performance. Riding the mids shifts your weight and gives better control of the bars. You can drop a knee and even get off the seat if you need to.
With forwards you don't have the same kind of balance. It's a totally different feel to go into a corner hard with your ass dragging and your feet out in front of you rather than under.
I tell people the D is the Jekyll & Hyde of V-Rods. You ride the mids for fun, sporty riding, and throw your feet forward and short-shift for leisurely paced riding. It does both quite well.
I have plans to have both using one of the methods I found here, just haven't gotten around to it yet.
Adding Arnott's air ride is even better. With the air ride you can keep the D'x ground clearance no matter what you and/or a passenger weigh (within reason). Keeping the mids and highway pegs keeps you ready for anything.
Having dual controls with the air ride would be the ultimate.