You can completely change the upcoming draft class in dynasty mode. I used it to put in this years upcoming rookies, and it worked fine.
Here's a tutorial (by misow, I think) on how to change the class, using Andrew Bogut as an example. It's in another language, but you can see what he's doing. You might need basic editing knowledge. If you need more help, PM me.
You don't have to start a new dynasty though. Just look at upcoming rookies, find whoever's expected to be drafted at your pick, and edit him via dbf. Name, nickname, skin, height, weight...anything.