Are there any cleats (for SPD-SL) that convert the pedal to a regular flat platform for regular shoes? I have a road bike that use Shimano 105 PD-5800 SPD-SL pedals and they are wonderful when exercising. However I would like to be able to use the bike with regular shoes for more casual use of the bike, but I also don't want to exercise unnecessary wear and tear on the pedals by not using a cleat. Are there any cleats (for SPD-SL) that convert the pedal to a regular flat platform for regular shoes?

I know that this question is similar to this one but I ask for a special cleat that converts the SPD-SL pedal to a regular flat platform and not a hybrid platform. I want to keep my Shimano 105 PD-5800:s since I really enjoy them.
For a ready made part, see Fly Pedals.

This is essentially just a metal platform, which you bolt cleats onto, then clip them into your pedals. They are threaded with holes for 2-bolt or 3-bolt cleats, so should work with most mountain bike or road bike clipless pedals (including SPD-SL).

Note these are not yet available, but you can pre-order them from the Fly Pedals website. Some more details on Fly Pedals on Kickstarter - that page says delivery from end of July 2014.