Here's a suggestion: design the SDK such that calling a method returns you everything you need to construct the REST call yourself: the verb, the url, the query params, the form params, and perhaps some headers.

    case class HttpCall[OutputType](
        verb: String,
        url: String,
        queryParams: List[(String,String)],
        formParams: List[(String,String)],
        resultType: Class[OutputType])

    trait Api {
      def getMyTasks(): HttpCall[List[Task]]
      def getTask(taskId: String): HttpCall[Task]
    }

The SDK can also provide a driver for making the http calls:

    trait Driver {
      def call[Out](httpCall: HttpCall[Out]): Out
    }

So now api invocations look like this:

    val myTasks: List[Task] = driver.call(api.getMyTasks())
    val aTask: Task = driver.call(api.getTask("foo"))

What's nice about this design is that the consumer can write their own driver if they don't like yours. Prefer asynchronous over synchronous? No problem!

    trait Driver {
      def call[Out](httpCall: HttpCall[Out]): Future[Out]
    }

Everything in the article except for grep-ability can be achieved with this kind of design.