You mean using a VGT as an exhaust brake? From what I hear, it works great.
Banks does make a plug-in module, but you can do the same thing with a EFILive tune. Most tuners will put it in on request. That does require a LLY (2004.5) or newer, though.
Like mentioned in the other thread just get efi with a dsp2 switch and a small tow tune with turbo braking. Or get a small tow tune flashed in and just drive that.