Override JSON deserialization

I'm trying to override the part when the JavaScriptSerializer creates a new instance of a given type when deserializing.
My situation is that I'm caching a list of data in the SessionState and I have a WebService that updates one specific item.  To make sure that the specific item is updated on the session, I would override the instanciation and return the current instance in the SessionState.
Is there anyway to do so other than creating a JavaScriptConverter and handling the deserialization manually?


Thanks

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