Take a look at www.franktalk.org there is a guy onthere using iner tube as a c**kring, because he has a leak, now this could be the same as your boyfreind, could be worth a look at and just may do the trick.
Good Luck
Bummer city - you may have to get him to a surgeon for reconstructive surgery to repair the broken vein.If it was years ago, then reconstruction may not even be an option, but he probably has harvestable sperm, so you could try artificial insemination