I bought a shoe loop for the Nike + sensor since I got some shoes that didn’t have the slot for the sensor in the sole. I attached it, pried the sensor out of my other shoe, and put it on. I was slightly worried it wouldn’t register, but it did, keeping pace about like it did in the base of the shoe.
I got an Action Pocket that was $10 and it holds the sensor in a small front pocket, and then velcro loops to shoelaces. It makes it easy for me to move the sensor to either pair of shoes, which I like.
Here it is on my trail shoes: