[ptx] missing a piece of sky... howto fill?

[manouchk]

Hi

I assembled this photo and happens that that some part of the sky is missing.

http://emmanuelfavrenicolin.free.fr/Public/Divers/Snapshots/p2150026_Cristo.jpg

Instead of going back and take a bettre shot, I'd like to know if you guys, 
have an expert advice to give to me?

Is there is a way (a soft) that allows to stretch parts of a image? It would 
stretch the border of the image, like if it was on a plastic and that the 
central part was maintained in place...

When there is sky on the upper part, I used to copy the sky and magnify it and 
reuse it which give a not so good but a "reasonable" result. In this case it 
is not possible!

EMmanuel.