I have conquered the need to do something like this:
'appUrl' => 'http://localhost/myapp/',
This is the absolute path, where my Application resides.
After that, i can use it to set a path relative from this one:
$image = Yii:app()->config['appUrl'] . "/images/myimage.png";
At the moment it raises an Exception in framework/base/CModule.php(404)
because there is no private Variable appUrl, but i fixed this for my purpose.
Does it make sense to apply this "feature" in future Yii Versions?