The custom card views would be expressed by the HTML that you have set in the $new_timeline_item
variable.
You can design the HTML using the Mirror API Playground at https://developers.google.com/glass/tools-downloads/playground
You would set this into the $new_timeline_item variable with something like
$html = '<article class="photo">'.
' <img src="attachment:0" width="100%" height="100%">'.
' <div class="overlay-gradient-tall-dark"/>'.
' <section>'.
' <p class="text-auto-size">Based on Hybrid Template</p>'.
' </section>'.
'</article>';
$new_timeline_item->setHtml( $html );
The img URL of "attachment:0" means to use the first attachment as the image. The rest of the HTML was based on the HTML generated by the "Hybrid" template on the Playground - you can adjust as necessary.