I tried this a bit earlier, but I didn't get it to work. I hoped someone else would answer but, yeah...sadly, if you give them only the launcher, they'll run around with empty hands, and only shoulder the launcher when they're about to fire. It seems to me the AI -never- use the "run with launcher on shoulder" animation that's new in ArmA, as far as I could tell at least. Even short movements prompted a complete shouldering-reshouldering action.
If it's just for a cutscene or something, you can try using the playmove animation. Here're the animations (from the BIKI):
AmovPercMrunSlowWlnrDb - Run backward with launcher
AmovPercMrunSlowWlnrDbl - Run backward left with launcher
AmovPercMrunSlowWlnrDbr - Run backward right with launcher
AmovPercMrunSlowWlnrDf - Run forward with launcher
AmovPercMrunSlowWlnrDfl - Run forward left with launcher
AmovPercMrunSlowWlnrDfr - Run forward right with launcher
AmovPercMrunSlowWlnrDl - Run left with launcher
AmovPercMrunSlowWlnrDr - Run right with launcher
Sorry we couldn't help any more!
Wolfrug out.