Use the WordPress media modal to add gallery shortcodes to custom meta boxes

gistfile1.js

jQuery(document).ready(function ($) {
	// Set the original handler, since we override Core, we need to fall back to core if we're not doing stuff our selves
	var _custom_media = true,
		_orig_wp_media_insert = wp.media.editor.insert;

	// Any input field wit hthe class 'theme_custom_media' will trigger our custom behavior
	$(".theme_custom_media").click(function (e) {
		var button = $(this);
		var id = button.attr('id').replace('_button', '');
		
		_custom_media = true;
		
		// We take control of the media managers 'insert' function (it only sends the html intended for the editor)
		wp.media.editor.insert = function( html ) {
			// If we are doign a custom media handling, do this
			if ( _custom_media ) {
				$("#" + id).val(html);
			} else {
				// If we arent' doing anythign custom, we return the original Core function and all is well
				return _orig_wp_media_insert( this, [html] );
			}
		};
		
		wp.media.editor.open(button);
		return false;
	});

	$(".add_media").on('click', function() {
		_custom_media = false;
	});
});