for various reasons, here at Sitefinity team, we are not big fans of sessions. That being said, in Sitefinity 3.6 we have included an option to turn off the ViewState for a page. All you need to do it go to Sitefinity > Pages, select a page, select Properties tab, expand More Options and you will find the checkbox there which states "Disable ViewState".
I hope you will find this information useful. Let us know if there is anything else we can do for you.
All the best,
the Telerik team