Nike+ product is a marvellous product, but without the shoes.
After relentless google, I have found some ideas from the net & youtube about ways to detach Nike+ from Nike shoes in the most economic way.
I feel this is the best for me, a Nike+ Sensor in a ziploc bag, fold it and slot it thru the shoelace like below. What's more, it's weatherproof and no issue of discomfort. To have 100% accuracy, just calibrate it.
Now, every shoes is Nike+ Enabled!