He should drink lots of water all the time (to prevent future ones from forming). They can do something called lithotripsy (sp?). I think that is non-invasive. They have lots of other ways besides surgery. It depends on the type of stone, size, location, etc.
Someone I know just had a stint put in the kidney to help a stone pass and to help the kidneys function better. The stint was in for 2 weeks and this helped a lot, but this was a surgery and then another one to take the stint out. This person has had stones for her whole life, many times, many ways of getting rid of them. They are no fun. For her, she is just prone to forming them and no matter her diet (which is supposed to be low in calcium, since her stones are primarily calcium), water intake, etc, she just forms a lot of them.
She said that passing them is worse than childbirth and can't imagine the pain for a man

Hope your friend has a quick painless solution soon!
eta: I am obviously not a doctor, this is just from my personal experience!!
HTH!
Jenn