Most players can't put a consistently good swing on the ball, so in a sense you're looking for the club that forgives him the most. You are trying to give him a club that minimizes his misses. Many club companies have portable fitting systems that are operated by club professionals and professional club fitters. The advantage of going to a club professional for a fitting is that he is likely to have several brands of clubs for sale, and may have a fitting system for more than one. This means that you won't be captive to a particular club maker, and may mean that the correct driver for your swing will come from one club maker, the fairway woods from another, and the irons from a third.
Ping has a system that is fairly standard for the business.
The fitter takes static measurements, such as height, wrist to floor distance of the lead hand, wrist to the longest finger, and the length of the longest finger. This helps to determine shaft length and grip size. The fitter also will want to know the average carry and roll of your driver and the average carry of your 5-iron. He then watches your ball flight and looks at the marks on the impact tape on the sole of the club. The Zevo fitting system is a small, portable version of Callaway's big box.