how to post arbitrary json object to webapi

How do I / is it possible to pass in a json object to a webapi controller (POST) and not have a class to map it to, but rather handle it as arbitrary content?

So if I pass in from my client like so:

        createRecord: function (model, data, callback, callbackParams) {
        var request = jQuery.ajax({
            type: "POST", // default = GET,
            url: '/api/' + model + '/',
            data: data,
            contentType: 'application/json',
            success: function (msg) {
                $('#results').text(msg);
                if (callback) // only fire a callback if it has been specified
                    callback(msg, callbackParams);
            },
            error: function (jqXHR, textStatus) {
                alert('Request failed: ' + textStatus);
            }
        });
    }

and data is something like:

{ "_id" : ObjectId("5069f825cd4c1d590cddf206"), "firstName" : "John", "lastName" : "Smith", "city" : "Vancouver", "country" : "Canada" }

My controller will be able to parse it? And next time the data may not match that signature (eg:

{ "_id" : ObjectId("5069f825cd4c1d56677xz6"), "company" : "Acme" }

In my controller, I have tried:

public HttpResponseMessage Post([FromBody]JObject value)

and:

public HttpResponseMessage Post([FromBody]string value)

and (because this is actually to work with a mongo db):

public HttpResponseMessage Post([FromBody]BsonDocument value)

but it looks like the object mapper wants to map to something other than string...