Found this over on Instructables.com, will get around to building one myself once I get over my laziness. Scoured the multitude of designs on the site but like this one since the weight rests mostly on the back tire with the front wheel more or less keeping the bike in balance. The guy has a 2-bike version posted also.
http://http://www.instructables.com/...s-single-bike/
Aloha,
Huladog