I've got an iMovie HD question. Can anybody help me?

So basically, I'm wanting to do a ghost movie where the main character is transparent throughout the whole film. 
 You'd think I'd just have to film a "empty" scene and then film the same scene with me in it and then simply overlap them. 
 
Well this works great and all, but the overlap transition can only last for a maximum of like 10 seconds. So you get an empty scene and then I fade in slowly and then the remainder of the scene is just normal me (solid).
 
I want an entire scene where the 2 clips play together making me transparent the whole time.
 
Is there anyway to make this happen? Hope the question makes sense.