You can get the towbar kit for the GTI, although it's probably not recommended if you're upgrading the 18" wheels etc.

If you're getting the genuine VW towbar kit, then when the actual towarm is not installed, I don't believe that you can see that you have a towbar kit installed at all. Please verify this with your dealer, but the entire towbar amount actually goes up inside of the rear bumper so that it is not seen from behind the car. The towarm then pushes up into that and you clip it in to secure it for when you need it.

It's a GTI, so it'll look ugly whilst you have the towarm in