Nope theres nothing on the Caddy that works other than the calipers themselves and as has been pointed out they need a little bit of a fettle to sort out that is......
1. Removal of the long hard black connecting line from the caddy caliper and replace it with the curly S shaped connecting line from your GTI rear caliper
2. Removal of the fixed bracket on the back of the GTI Caliper (Not the movable handbrake "lever") and transplant it onto the Caddy caliper
Theres no need to worry about the Master Cylinder dont forget in essence we're getting S3/R32 rear calipers in terms of piston size and they dont get an MC upgrade.
Just a refresher, Diameter counts for nothing in braking so GTI Rear Radius is 286/2 = 143mm................S3 rear radius 310/2 = 155mm
So a 8% ish rear reduction in radius over an S3 setup for a 7ishKG axle reduction in weight.......
Dont get me wrong if you're going BIG brakes on the front then the S3 upgrade or even bigger is required to maintain balance.
The caddy mod just complements the NQSBBK really well, dynamically works and doesnt cost a fortune and has reasonable renewables.
The later BOSCH calipers of the 2009- DONT work, you can tell the ones you need they just look exactly the same as stock GTI ones they just need some paint.
In fact some already have them and nobody would ever know