You can now get the additional loom required to fit cruise control to a 1.8t (and other models) as a genuine VW spare.

 For engines with the 80-pole ECU plug (Engine codes: APE, AXP & BCA)
1J0.971.425.B

For engines with the 121-pole ECU plug (Engine Codes: ARZ, ATN, AUM, AUQ, AUS, AZD, AZH, AZJ, BAD, BCB, BFQ)
1J0.971.425.C

The wiring goes as follows:

Engine Code: APE, AXP & BCA (80-pole plug)

Pin 24: Black/White Wire

Pin 25: Red/Yellow Wire

Pin 39: Blue/Grey Wire

Pin 50: White Wire 

Engine Code: BAD (121-pole plug)

Pin 49: Blue/Grey

Pin 51: Red/Yellow

Pin 52: White

Pin 55: Black/White

Engine Code: BFQ (121-pole plug)

Pin 66: Red/Yellow

Pin 67: Blue/Grey

Pin 68: White 

Pin 69: Black/White

Engine Code: ARZ, ATN, AUM, AUQ, AUS, AZD, AZH, AZJ & BCB (121-pole plug)

Pin 38: Black/White

Pin 57: Red/Yellow

Pin 75: Blue/Grey 

Pin 76: White

Hope this helps