AFAIK, OData feature provided by wM is not quite matured, you cannot consume the URL (like we do for WS-WSDL), if you are unable to use the SAP connection as an external source then only option left is to write wrapper services using client:http (_get,_post,_put,_delete)
Not sure if others have any idea, but lets wait and watch.
#Integration-Server-and-ESB#webMethods