One approach you can take is to use Data Caching. The data would be persisted on the server as XML files. You would use the SessionID to isolate the caching on a per session basis. Keep in mind that this approach does not work on web farms. Here is a link to an article that explains how this would work:

http://www.dotnet247.com/247reference/a.aspx?u=http://msdn.microsoft.com/msdnmag/issues/01/12/cutting/cutting0112.asp

>All,
>
>I am looking for a way to persist a dataset between postbacks without using session variables.
>
>Is there a best practice for this?
>
>TIA
>
>Rex