Any method to do it without surgery would be even more invasive than surgery. Off the top of my head, the only thing I can think of[1] is inserting a long flexible tube down the urethra, hoping that it ends up in the right place (it's not very helpful if it ends up in the bladder), and then sending RISUG through it. Likely to be very painful and not work particularly well.
[1] There are only so many ways to get to the vans deferens without surgery, so I'm not too worried about missing something obvious.
Or nanobots, I suppose, whenever we get those. That doesn't seem likely to be any time soon, sadly.
If this procedure gets popular enough to change humanity, I'm sure it will. Right now, it's being performed by only one doctor in India and he's not accepting help.