I just got back from a business trip and had to deal with the same problem. What I ended up doing was a modified crossfit type routine. I did 10 push ups, followed by 10 body weight squats, followed by walking lunges across my hotel room followed by 10 crunches and did this for 5 rounds. It must have worked because my legs were a little sore the next day (I think it was the walking lunges).
I was lucky that I was only gone for a few days so didn't feel too guilty about not being able to do pullups. If you're looking for a good substitute try taking a hotel bath towel, face the bathroom door edge-on, loop the towel around the handle, grab both ends of the towel and with your feet braced against the bottom of the door, let yourself slowly go back and start rowing. Make sure you you really bring your elbows back as you row (imagine you're trying to elbow someone who is behind you). I guarantee you'll feel it the next day :)