SharePoint REST service to add an exsiting site content type to a list/library

Trying to use SharePoint 2013 REST Service to add existing site content types to a list/library. Below MSDN article suggests that the POST method is available but does not say how to use it.

http://msdn.microsoft.com/en-us/library/office/jj246793%28v=office.15%29.aspx#postsyntax_htm

POST http://<sitecollection>/<site>/_api/web/lists(listid)/contenttypes/add(parameters)

How do we create the body for this rest call?