Diesel Power Source recently released a VNT housing for S400 series turbos. If you want to switch to a VNT that's the way to do it because there's no computer programming required.
For everyone asking why someone would want to switch to a VNT, the answer is pretty simple: they're better. Your turbo will never reach its full potential without a VNT. The problems they have are directly related to the way they're used with the EGR systems. Get rid of that and set them properly and you'll never want anything else...except maybe compounds.