When I over-do on carbs my palms and feet perspire heavily. When I cut back on my carbs my perspriation level drops dramatically. Have him keep a food diary for a week. (If he's not following his food program he may balk at this.) Elimination of all refined carbs and high glycemic carbs may just do the trick. [ie. sugar, white bread, flour, breading on fried foods, white rice, mashed potatoes, cereals like corn flakes (better to stick with whole grains like shredded wheat or cheerios or oatmeal), veggies like corn etc.]
If he does that and still has the perspiration problem you may want to check with a podiatrist. There may be something stronger that we don't know about he could try.
"As one goes through life one learns if you don't paddle your own canoe you don't move."
"Madness takes its toll.
Please have exact change."