If he tends to play a lot of his golf at his home club this might not be an option but a golf gps could be a good present. There are subscription based devices like Sky Caddie (courses are physically walked by mappers) or non subscription based like golf buddy, garmin, sonocaddie etc. Obviously these can be expensive but if you are pitching in then it might be ok.
I’d stay away from buying clubs due to what’s already been highlighted above but booking a custom fit session at a Mizuno fitting centre (for example) for a new driver or fairway wood or rescue hybrid could be a good option. The custom fitting session is free and you can buy the club through any Mizuno stockist locally. You can use your local pro for a custom fit session for any other brands he stocks as well.
Also how about a very smart leather holdall-a lot of golf folk take these with them to hold shoes/waterproofs etc etc. Doesn’t have to be a golf brand either.
Would he normally spend an awful lot of money on golf clothing? If not a very nice pair of shoes (ecco for example) could be an option. Depends whether you want to buy him something that is ‘disposable’ or not.
How close to the next open venue does he live? Would he enjoy a season pass for the open?