Someone was nice enough to write a script for toggle aim/crouch and sprint.
Get it from this link http://forum.ea.com/eaforum/posts/list/421736.page
Ty Zulu useful link
Two options are unzipped, crouch/walk and crouch/walk/aim, its a godsend as you don’t need to keep pressing L/Ctrl to crouch.
Just unzip to a folder someplace and then active which ever you want before you play.
Semples