Use "custom" objects as Extender Control Properties

When creating an ASP.NET Extender Control (using ASP.NET AJAX and the AJAX Toolkit) you can add custom properties to your Extender (using the ExtenderControlProperty attribute) that get passed down to the client. Well, this is really cool and all, but you are restricted to using the “standard” variable types (string, int, bool, etc.); unless of course you want to create your own custom TypeConverter to convert your custom objects to JSON.