Migrating to Microsoft Ajax RTM - missing Json Converters

I recently migrated a large project from an old ATLAS CTP to the MS AJAX RTM were I was using web service calls to get data via typed datasets. The lack of JSON converters for DataSet, DataTable and DataRow was a real problem. Lots of 'System.InvalidOperationException: A circular reference was detected...' errors. Here is how I got around it with minimal fuss.