rubberbands is your solution...
there is a slightly more expensive alternative to rubberbands, but its also some kind of elastic band thingy with a ball at the end. Saw it on the strobist website...
Don't want sync cord? Only way is to have a wireless trigger mounted on your hotshoe. For the rich, no problem. Heh. Just buy pocket wizards. Or... check if your camera's built-in flash supports commander mode.