First of all, I would like to compliment the person(s) who came up with this great Marketing Campaign!
From what I have seen there are many winners.
The way I would approach it, and I am not sure if any one else has used this idea or not, is I would like to see 4 people on the cover, 2 male and 2 female.
These folks would represent the 4 authors of the book. Not quite sure which 4 since they all look good to me, so I would leave that choice up to the authors (Elisabeth Freeman, Eric Freeman, Bert Bates and of course Kathy Sierra).
Sounds like a Pattern to me!