This is the final product: A surprisingly strong magnetic key hook that takes just a few minutes to do. It is ridiculously inexpensive and does not involve replacing your existing plastic switch plate. I did not even use tape or glue. This is so easy I debated not even posting it. However, someone else may find the information useful. Keep in mind that you need to have the cheap, ubiquitous, builder's quality, plastic switch plates to make this work. The magnetic force will easily cross a plastic switch plate. Any other switch plate is YMMV.
When you are done, you can turn the light out and take your keys. I already have 2 key hooks mounted on the wall next to the light switch. However, my wife has insisted on using both hooks to wrap the 2 rings she has on her key chain over top my keys. I constantly need to take her keys off the hooks to get to my keys. Instead of make a Federal issue over it, I made the switch plate into a magnetic hook for my car key.
Step 1: Begin with a strong magnet and something to wrap the sides
Step 2: Put magnet in cap and put it behind plate
I did not cut the power to the switch but I advise others to do so. Realize where the wires are attached to the switch. There was one screw on that side of the switch for the hot wire. Therefore, I put the magnet next to the green ground screw at the bottom. That's it! You are done! The result is a surprisingly strong magnetic hook for keys (as seen in the first image).
Now I don't have to constantly take my wife's keys off the key hook to get mine. Yea.