I've done the same, checkin online, but no printer. Due to a traffic accident that stopped the freeway, I ended up at the counter only 12 minutes before the flight at ORD. I saw there was no line at security, and L2B is right on the other side. I asked permission to run for it, and that agents were super cool. While they said they couldn't hold the aircraft, they called the gate to let them know I was on my way. Gate agent met me at security and helped speed things up, and they still had my first class seat for me.

I think the biggest thing that helped me was I asked for permission. I told them I know I'm late, got held up due to an accident, and if they would be kind enough to let me run for it. I think that approach worked better than those who act "entitled" to be late, and demand service even though they're outside of stated policy. AS did me a favor in this case, and I greatly appreciated it!!