here you go:
https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch16.html
https://mtnphil.wordpress.com/2011/10/18/wind-animations-for-vegetation/
Two articles specifically on the vegetation system in FarCry. I was interested when reading your post because I thought the easiest option would be via a shader. The second article is a detailed breakdown on the CryTek/FarCry article (which is the first one). It also includes code for a test case.
https://www.youtube.com/watch?v=Mb5QVoqFkKo
https://skydrive.live.com/?cid=32374812f02e440e#!/?cid=32374812f02e440e&sc=documents&id=32374812F02E440E%21153
It would be pretty epic to see Megatextures combined with the ago and then a procedural real time grass system like described in http://jcgt.org/published/0004/01/02/paper.pdf