What is the best way to trap my cat so I can get him back? (repost, please help!)?

Contact a local cat charity / animal rescue organisation and get them to lend / rent you a humane trap, (this is like a big pet carrier cage with a pressure plate, that closes the entrance, just in front of a food bowl). Get your sister to bait the trap, and call you when the cat is caught in it, then collect your cat. Your sister will not have to touch the cat (providing you get there soon enough) and the trap can be used as a cat carrier until you get home.