I watched someone on an airside bus do just that but to themselves and with a carabiner not a zip tie. He had boarded the bus almost last and the pushed his way through the assembled masses with his rucksack hitting all and sundry. There was a satisfying click as we took a bend and the carabiner on front (or the back depending on your point of view) attached itself to a handrail. There were a few smiles when that happened.