Discretely, yes you "should" be able to do it. By the books though, your guest is supposed to leave with you when you leave the AC lounge. I've never noticed anyone actively checking if my guest is leaving with me or not, but if you walk out 5 mins after checking in then it might be a bit obvious. An excuse like Duty Free would probably do if questioned but if the lounge agent were overly zealous then they "could" boot your friend at some point when you don't return. Unlikely scenario but possible.