Can iPhone 4S' digitizer be fixed?
The LCD and the digitiser are a single integrated piece and cannot be separated for repair. As Alex said above you would have to replace the entire lot. 

This forum post over at iFixit a very popular iPhone/apple/computer repair blog and shop highlights the fact this cannot be done. 

http://www.ifixit.com/Answers/View/25507/Can+I+separate+the+glass+from+the+LCD+screen