You'll be pleased to know that this one is pretty straightforward. Your colleague just has to present his UK licence and medical at the nearest FDSO and he will get a brand-new FAA licence free of charge in a couple of minutes. The only rating that causes difficulty is the Instrument Rating. This will not be honoured automatically, and requires a further ground exam.
http://www.faa.gov/avr/afs/faa/8700/...2/2_029_00.pdf gives chapter and verse
Hope this helps.