You could override default templates paths thanks to Media. The filter above sets different paths for admin requests (in config/bootstrap/media.php).
Dispatcher::applyFilter('_callable', function($self, $params, $chain) {
$next = $chain->next($self, $params, $chain);
if ($params['request']->admin) {
Media::type('default', null, array(
'view' => 'lithium\template\View',
'paths' => array(
'layout' => '{:library}/views/layouts/{:layout}.{:type}.php',
'template' => '{:library}/views/admin/{:controller}/{:template}.{:type}.php'
)
));
}
return $next;
});