What a beautiful image. I`m sure he will be fine for one evening/night, although I would make absolutely sure that your sister (what age is she?) doesn`t try and spoil things for you by making you worry unnecessarily. Otherwise maybe ask a friend who isn`t that hamster savvy and won`t actually want to handle him.
Put a sign on the cage saying, "I bite"!!!! That should be a good enough deterrent!