Unfortunately, when there's nothing there to work with, there simply is nothing there to work with. Photoshop is a great program, but it doesn't work miracles.
A good example of this is something that I'll probably end up posting on my site, once it's done...don't go there, yet, it takes forever to load and it isn't finished...but for right now, I'll just post the starting file.
It started as a piece that was given to me during my days at Kinko's...it's a picture of a lady's mother as a child, but her face was scratched out by a racist woman

(also in the picture, apparently) and she simply wanted the face replaced...what was necessary was something not in existence...a picture of the woman's mother at the same age.
Solution:

a picture of HER (the client) at the same age, since they apprently looked exactly the same...I just had to replace missing information.
The other thing that works is to simply paint in what you think should be there...Photoshop's painting tools and features are absolute dynamite, and I've seen them turn talentless people into incredible artists, but the work still needs to be done...it can't be done automatically.
Now, I don't know if this kind of advice will help, but like I said, if there's no data, there's no data...
Perhaps if you posted the photo you're working on I may be able to find a better solution for you.