I am an ex-drag racer and have been around nitrous since the late 70's. Just prior to getting involved in the Crossfire I was very active in the Mini Cooper community and quite few cars ran Nitrous dry systems, meaning only nitrous was being injected and the stock computer and fuel injectors were capable of correcting the Air fuel ratio. Here a link to a sytem that some of the Mini Cooper S guys used with no reported problems. With patience, and careful attention to detail, you could do this yourself.

http://www.zex.com/Pages/124/Dry%204...0Cylinder.aspx