client.json

        "create_ticket": {
            "httpMethod":"POST",
            "uri":       "tickets.json",
            "summary":   "Create a ticket",
            "parameters":{
                "data":        {
                    "type":       "array",
                    "location":   "body",
                    "description":"Ticket JSON",
                    "filters":    "json_encode",
                    "required":   true
                },
                "Content-Type":{
                    "type":    "string",
                    "location":"header",
                    "static":  "application/json"
                }
            }
        }

client.xml

        <command name="create_ticket" method="POST" uri="tickets.json">
            <doc>Create a ticket</doc>
            <param name="data" type="array" location="body" filters="json_encode" doc="ticket JSON"/>
            <param name="Content-Type" location="header" static="application/json"/>
        </command>

usage.php

<?php
    /**
     * Creates a new resource, returning the updated $object
     *
     * @param string          $resource
     * @param AbstractCommand $command
     * @param ModelAbstract   $object
     */
    protected function doCreate($resource, AbstractCommand $command, ModelAbstract $object)
    {
        $command->set('data', array($resource => $object->toArray()));
        $data = $command->execute();
        $object->fromArray($data[$resource]);
    }