I just read a great article about crop-dusters around the United States. Of course I forget what magazine, but anyways, I digress. The suggested method of "getting in" is you gotta work the grunt jobs within an operation initially, to get a better understanding of what goes on anyways. There are "Crop-Dusting" schools down south somewhere, but maybe only 20.
So I guess tell your buddy to get his private pilot license, preferably in a tail-wheel aircraft, then build the time to get up to the commercial. Hang-around some dusting operation and see what happens. Weird how I just was reading about this a week ago, but that's pretty much what those guys said. There is a huge demand for people crazy enough to do that kind of flying BTW. I'd do it if I were local to the southern areas where it's popular.