We don't currently have a way to set the Twitter card tags individually. For now, you'd need to make an edit to our code to force the tag. To do so, edit the /libraries/sourcecoast/OpenGraph.php file. Around line 394, you'll see:
else if($this->name == 'og:type' && !in_array('twitter:card', $skipGraphFields))
$graphValue .= '<meta name="twitter:card" content="summary"/>' . CARRIAGE_RETURN;Update away!
I hope that helps,
Alex