Passing multiple Parameters to a Web API Controller

Single parameters work fine in either of these RPC scenarios and that’s to be expected. ModelBinding always works against a single object because it maps a model. But what happens when you want to pass multiple parameters?

Consider an API Controller method that has a signature like the following:

Here I am asking to pass two objects to an RPC method. Is that possible? This used to be fairly straight forward either with WCF REST and ASP.NET AJAX ASMX services, but as far as I can tell this is not directly possible using a POST operation with WebAPI.