Here's a place that claims if it has an engine - they can put a turbo on it.
They're located in Seattle. Like I said, I'm not interested in doing it, but if you're serious then someone should contact them to find out. They do have a white e90 on their website with some funky exhaust.
2015 GTI S, 6M, LP, Volk TE37SL 17x8.5, Michelin PSS 245/40, HPA SHS Coil-Overs, Peloquin LSD, Sachs SRE, Eurocode F/R Sway Bars, SuperPro Control Arms, Remus Catback, APR Stage 1 Tune, APR CAI, Aero Force Gauge Pod, APR Boost Gauge, Kersher Front Lip, Short Shifter, Tyrolsport Deadset, Stoptech BBK, HPA Dogbone
2008 BMW Z4 3.0si Coupe - because racecar