I can't really sign off on this. It's not a terrible suggestion to workout more, but honestly man, I'm WAY leaner than you are, and I only go to the gym 3 or 4 times a week. Sometimes less. Building muscle mass and eating properly are the 2 most important factors in getting lean. Spending lots and lots of time in the gym sweating isn't particularly effective.
I do agree that bicep curls and tricep extensions as the basis of a program will not help him reach his goals either.
I'm a firm believer that a very basic program centered around compound movements, combined with a solid nutritional plan, is the way to go for most relatively healthy adults.