Probably not, really. They can add notes and such, but I don't know of any carrier that can actually combine PNRs into one. The systems simply aren't built that way.

If you're traveling together anyways then he can get most of the benefits like security and boarding priority. And any phone agent should be able and willing to seat him next to you, even in the $$ seats, without charge. The only thing that wouldn't likely work is free bags.