Can It Be Done With Balls Alone?

I've got a question. In the story 'Humping All the Time' the girl says that she can get off using only her clit not her vagina. As we know the clit is comparable to a penis in a male and a vagina to the scrotum.

What this girl experienced is similar to a male's orgasming with just his erection. I know some women cum only with vaginal stimulation as there is a g-spot within.

My question: Is it possible for a male to cum with only scrotum/ball sack/ball stimulation, without messaging his cock? Is there a male g-spot down there anywhere? In college my roommate was obsessed with getting her boyfriend off that way without success. Does anyone know of a way?