Today I came across a video by "nikeplusrunners" who came up with an easy and free way to use the Nike+ sensor without using Nike shoes! I've tried running using this method and my Nike GPS sportwatch has no problem detecting it during my entire run.
Step 1: Place your Nike sensor into a platic bag or zipper bag
Step 2: Slot it all the way in between the tounge of your shoe and the shoe laces.
You won't even feel it during your run. It's that easy! And it's water resistant too! There's no need for any costly sensor pouches or drilling your shoes...