No need to get real fancy. I use a welding rod with the flux buffed off, and have rounded the tip over so it won't scratch anything. Get the piston close to the top, set the wire in through the plug hole. Slowly turn the engine over by hand with a Johnson bar, just watch the wire, it will show you when your at TDC. Of course, this isn't nearly as sexy as a threaded piston stop, but it doesn't cost like one either!