There is a existing extension for infinite Scroll, however it is not been updated in 3 years.
I have revamped the extension to include support for infinite scroll 2+ jquery plugin including callback support and other features . It is available here
github.com/manquer/yiinfinite-scroll
Let me know if you have problems using it 
Cheers
Mani
P.S: Sorry about the code formatted link, I am not allowed to embed links being a newbie even with code!!