Just further to my comment, if you have not figure out how to do this yet, I hope below instructions will help.
Purchase a Nike Plus sensor case or silicone pouch using a reputable online retailer such as Amazon or EBay. You can also visit your local sporting goods store to see if they have any sensor cases or pouch options available.
Secure the Nike Plus sensor into the holder or pouch and strap it to the tongue of your shoe or around the shoelaces as shown in the examples on the Amazon listing (see Resources).
Sync your iPhone or iPod device to the Nike Plus sensor. Both devices should have a built-in Nike Plus receptor so you don't have to attach one to the bottom of your device.