The Mk5 R32 anchors will fit the GTI - you just need to make sure you get the caliper carrier from the R32 too.
Oh, and you'll have to have 18"s for the R32 anchors.
Just a quick add on for anyone thinking of doing this, if you have a puncture on the front the spare wont fit over the r32 caliper.
You would need to put the spare on the rear, the put the full size from the rear onto the front.