I'll start off by saying that I had no interest in putting a coin button on my cp (less is more).
I also don't want to necessarily tell all my friends where my shift key is (I'm using a KeyWiz) cause they'll end up changing the button assignments or something.
I've seen people do what I'm about to show before, but I don't think I've seen it done just like this (somebody will likely correct me on this one

).
The first thing I did was drill a small hole on the mech holder at location A. I attached switch B with a screw. You will notice that the microswitch has one of those levers similar to what's found on some joysticks.
In the second pic, you will see the switch activated. when the coin reject button is pushed, the side of the coin mech kicks out and engages the switch.
The ground for this switch (and the one on the other slot) will be wired through switch C. This will allow me to turn free play on and off.
Now the reason that I'm sharing this is that I think a lot of people (maybe just the newbies) have this same problem. I found the installation of this switch extremely easy (drill one hole) so I decided to pass it on...
aside: my cabinet is progressing well. I'm going to post a project announcements soon once I get this stupid Gallery program working on my site (if anybody is a gallery master and can offer some help, drop me a PM).