Technically, if you are going to stay in one city longer than a certain number of hours, 4 I think, it becomes a separate flight. But, with buddy passes, you are allowed to make one stop in each direction of your travel, as long as it's “on the way” (i.e. sort of in-line, or in the same direction, as your final destination). So, you should be allowed to just make an official stop in ATL on your way to PDX. You should also be able to stop somewhere on your way back, if you want. You are supposed to be able to do this even if you wouldn't have originally stopped in the middle city. For example, say you wanted to make a stop in Houston on your way. You would fly TPA-ATL-HOU on the first day, then the second day you'd go HOU-SLC-PDX (or perhaps even HOU-ATL-PDX). I've done this quite a few times.Also, a second 'secret' method: let's say you wanted to do this HOU example, AND spend a night in ATL. It's not really supposed to be done, but let's say you scheduled yourself on the last flight from TPA to ATL of the day. You would pretty much have to stay the night in order to get from ATL to HOU the next morning, right? And, let's say you got to the airport late in the morning, and had to go on a later flight...no one would really mind too much, although it could be possible for a stickler to mention that you violated the 4 hour rule, so this second method isn't really recommended.