Maybe it is not what you are looking for, but I had a similar problem and i solved it including JSON 2 to my application:
https://github.com/douglascrockford/JSON-js
Other browsers natively implements JSON but IE < 8 (also IE 8 compatibility mode) does not, that’s why you need to include it.
Here is a related question: JSON on IE6 (IE7)
UPDATE
the JSON parser has been updated so you should use the new one: http://bestiejs.github.io/json3/