By default HttpClusterServlet will manage the sticky session by "HttpSession" object. If you are getting any problem with that, we probably need to debug more.
1) Can you give me some setup details how you have set it up ..
2) Also if possible, use Fiddler and get me the fiddler output.
3) Why do you think that it is not doing sticky session,are you getting flipped to another node and session data is not avaible.
Also some traces of logs when it happen...