custom_vc_element.php

<?php
function free_and_premium() {
	vc_map( array(
		"name" => __("Premium", "js_composer"),
		"base" => "premium",
		"content_element" => true,
		"category" => "content>",
		"show_settings_on_create" => false,
		"params" => array(
			// add params same as with any other content element
			array(
				"type" => "textfield",
				"heading" => __("Extra class name", "js_composer"),
				"param_name" => "el_class",
				"description" => __("Content only visible for premium members.", "js_composer")
			)
		),
		"js_view" => 'VcColumnView'
	) );

	vc_map( array(
		"name" => __("Free", "js_composer"),
		"base" => "free",
		"content_element" => true,
		"show_settings_on_create" => false,
		"params" => array(
			// add params same as with any other content element
			array(
				"type" => "textfield",
				"heading" => __("Extra class name", "js_composer"),
				"param_name" => "el_class",
				"description" => __("Content only visible for free members.", "js_composer")
			)
		),
		"js_view" => 'VcColumnView'
	) );

	if ( class_exists( 'WPBakeryShortCodesContainer' ) ) {
		class WPBakeryShortCode_Premium extends WPBakeryShortCodesContainer {
		}
	}
	if ( class_exists( 'WPBakeryShortCodesContainer' ) ) {
		class WPBakeryShortCode_Free extends WPBakeryShortCodesContainer {
		}
	}
}
add_action( 'vc_before_init', 'free_and_premium' );