The demo pedals? Go to your lbs and ask for some. I bet they throw dozens of them away. They only last a ride or two. For a permanent solution, how about single sided pedals? Best of both worlds.
As I'm very happy with the sl's on my bikes I'd rather not change them out if at all possible. I just would like the ability to quickly change to platforms when it's time to cart my son around. I see that there are solutions out there for the SPD's but I don't see any for the SL's.
Right now I have to change out the pedals each time which is a PITA and can't be good for the threads.