Converting to JSON would be one technique you could use for serializing the data. I wouldn't have thought you would need to pass it though JavaScript though, that would put extra processing requirements on the client and break if JS was, for some reason, not available. You should be able to simply drop the JSON string into the hidden input (after encoding any characters that need to be represented by entities with HTML::Entities).

See my previous comments about GET length and the suitability of POST though.