Print a field in a set display mode
There might be a shortcut to this but I don't know it...

// Get the bundle settings.
$info = field_info_instance('node', 'field_name', 'content_type');

// Get the field render array
$build = field_view_field('node', $node, 'field_name', $info['display']['teaser']);

// And print it
print render($build);


Moving the display building logic to a preprocess function would probably be a good idea.