ASP .NET is allowed
Storing the values in hidden input fields is allowed
Query String is not allowed
POST request is not allowed
It is possible to store J
If the objects you're storing are big, or if you want to restore them precisely (which JSON certainly doesn't) then use http://rhaboo.org. Most libraries serialise large objects and arrays into a single localStorage entry, but that means decoding and re-encoding the whole thing at every little change, which means gradually worsening performance for loyal users. Rhaboo uses a separate LS entry for each terminal value in the object, and then adjusts or appends them individually, so you don't get that performance hit.
BTW, I wrote rhaboo.