How about a large frame revolver? Outside of revolvers there's always a Desert Eagle (at least they seem large to me).
Qwiks draw said:Like the suggestions so far. Split the difference would be a PT100 in .40 S&W.
The PT 1911 might be another choice and it comes in the .45ACP
There are special handgrips for large handed people put out by Hogue and Pachmayr. So it could be a case of buying what he wants and then just swapping out the regular grips with the newer larger ones. Some grips are rubber and others come in wood. SO there is a choice.
Custom grips can be pricey. Herrett's gun grips would work.