I had a bit of a dilemma recently where my financier had the truck and I wanted to go to the bike park. It's a bit of a haul to ride the 20" all the way out there. I'd talked about carrying it on my back while riding another bike with a friend, and suddenly that became a necessity. Here's how it worked:
The set up
Bungee corded the bars and cranks in place, and then strapped the whole thing to my back pack. She got back right as I was leaving, and snapped this picture (then restrained the dog):
Vicious Max approves
It worked out great, just have to be careful that I don't go through anywhere to narrow!