How to keep page alive without session time out for a required page.

Hi all we Know that we had an option to set a session time out value. when the session time value expires we had a problem to again reallocating the session values and session time out with a long process. For some we need to keep alive the session values. To solve this problem we actually increase the session timeout value. but this is not a correct process. Some time we may need to have more session timeout for some pages and less session time out value for some pages. At that time we will face the real problem. But we can over ride it very easily. How to Increase the session time out dynamically ????