System.Web.UI.StateBag is internal, a workaround?

[Jiho Han]

I was hoping to implement a customized viewstate management and was hoping
to use StateBag for this only to find out that its access level is internal.
No dice.
The class is not derived from control so no base.ViewState. It only
implements IStateManager.
What are the possible workarounds other than re-implementation of StateBag?

Thanks in advance.
Jiho