LOL, this is a pretty specific situation. I doubt it would be an issue with the airline, as you can gate check it. As for security, I haven't tried running a "double-wide"

through the x-ray machine, so I'm not sure. I guess worst case you can bring it and give it a go. If you can't get through security, you could check it at the counter (or leave it in the car).
PDX has two sides for security. Since Concourse A-C (on left side as you come from ticket counters, see map link below) is where most of the planes are, most of the time, it is easier to get through security on the Concourse D-E side (right side as you come from ticket counters).
Usually the lines are much smaller on the D-E side (unless Continental, United, and/or Delta are close to flight times), so try there first, as the TSA agents can take the extra time to help. However, if the line at one side looks long, have a peek at the other side. if they are balanced, no worries just go in the one you are in front of.
Once through security, there is a walkway that connects the two air sides.
Map:
http://www.portofportland.com/pdx_terminal_map.aspx
Have fun!
ETA: You know, now that I think of it, you may want to post this question on the Transportation board. Since the TSA machines are fairly standardized, you can ask if a double stroller fits through them. They'll know on there, and someone is likely to know how the TSA handles them, too.