I'll have to chime in here too-I tried to set my machine up for a public show once, and tried to set all of the games my machine supports (120) to free play. I'd say less than 1/3 of them had the dipswitches to do it, and there *always* seems to be at least 1 "gotta have" game that doesn't support it.
I even went so far as to try to auto-load cheat codes to drop quarters in for me at ROM bootup, but even then, some games only take 9 credits at a time, which would run out in a hurry during a party. It was a disaster.
After futzing with it for a couple evenings, I gave up and installed a button near the coin door.
Luckily for me, some previous owner of my cabinet had installed a lock bar over the coin door, so I already had a button sized hole to use.

-jeff!