Clipless Pedal Training Wheels

I was flipping through D's Nashbar catalog when I came across a piece of equipment I've been looking for but was told didn't exist:

"Nashbar Sneaker Adaptor - Clicks into any SPD style pedal, allowing you to ride without a cleated shoe. Black. (Pedal not included)."

Only $5.95 a pair. Woo hoo! This will allow me to put clipless pedals on my future road bike if/when I one. I'll keep these babies in my backpack. In case you're wondering why anybody would do that, just remember that I'm the same person who used to carry a pair of sneakers in my backpack in case of emergency. At least the adaptors are lighter.