Justin paints something for Ted & Blake's housewarming, Brian has it framed
I know it's a one-shot, Ted and Blake have their housewarming party, though I'm not sure if they bought a house or just re-did Ted's condo. Justin is living in New York and ships the painting he did for them to Brian ahead of time. At the party, he's pleased that Brian says it's from both of them, but then they open it and Justin sees that Brian actually did contribute framing, and the frame is like Justin imagined it should be, and he's really happy. And I think he did a similar one for the loft or Britin, too.
Does that sound familiar to someone?
EDIT: FOUND! It's Parallel, by stephmck. Thanks to court1429!