And to think, someone's reading and responding in the console forums. 
Well, you're reading, but you're sure as hell not answering his question.
Well technically, neither are you. I mean no offense to the ribbing but when you're calling the Console forum useless and then kinda hint that you want to charge people to play with your PS2, not much help is going to come his way.
But nevertheless there were some answers on this thread. I'll stop waxing about legality and so forth and tell you what I'm theorizing:
Games for the console were not designed to wait for a coin input. So no matter which route you go it's not going to be authentic. You can do what you originally said and wire the start button to the coin switch (but you should keep another start button somewhere for pausing and so-forth). It won't work too well with any game and it won't work at all with some games, but that's the simpliest way.
Perhaps there's something that can be done software side - kind of like the Playchoice 10 that, as you stated, will let you play the game indefinately for a set amount of time. If it can be done is not something I can say since I am not a programmer.
Then third is something hardware wise that'll set off, again as you stated, a timer that'll cut off the controls after a certain duration. Though that's going to be kind of awkward when time runs out and the game just hangs there waiting for input that never arrives (kind of like when you're friend unplugs the controller while in a heated death match).
Personally I don't think any of the solutions are worth the trouble, but I am curious to hear the device Dave K mentioned (so I won't rule it out completely).