So here's possible ways Andy can get to know the other characters:
Dalles and Andy both writers, so they could have met after working together on the same issue of a magazine one month. Maybe they both could have been stressed after the meeting and decided to get a drink after. It would be funny if this was after Andy, Ty and Angelique were hooking up, that way Dalles could have a reason to be fascinated and hang around the threesomers.
And if Dalles and Melanie were close at this point, he could invite her along to scout out the oddity with him for the first time.
1Saz: What ideas do you have for the mail clerk scenario? I have a pretty simple idea. A coworker of Ty's could have ordered caramel cupcakes from Andy, and steals asks for one. Loving it, he asks for Andy's contact information and then they meet up when she delivers/he picks up the cakes. Maybe he asks her out, but they could hang for a bit and Andy goes home and tells Angelique she's found the answer to their sex problem, haha
Not so sure about Jackson though. Is he going to be the second to the last addition, just like Barney?