What do you do when you can't use ViewState?

Question

I have a rather complex page that dynamically builds user controls inside of a repeater. This repeater must be bound during the Init page event before ViewState is

Answer 1

This also has issues, because I have to explicitly null the session value during non postbacks in order to emulate how ViewState works.

Why do you have to explicitly null out the value (aside from memory management, etc)? Is it not an option to check Page.IsPostback, and either do something with the Session variable or not?