Mame has supported clickable artwork for a while now, but it's not going to disappear when you move away from it.
Mame doesn't support simulated keypresses so regardless of what solution you find, it isn't going to work on mame anyway, unless you do it some convoluted way like using ppjoy to send simulated joystick presses and even then your chance of success is limited because all emulators are fullscreen directx applications. Anytime you click outside of a fullscreen dx app, it minimizes or worse.
I haven't heard of this touch buddy, it might work around that judging by the application, but again, if it's simulating keypresses then it won't work anyway.
Long story short, add a start button and coin button. You have room regardless of what you say because I've seen people cram a 6 button layout with micro coin/start on a cocktail control panel. You don't have to use full-sized buttons for coin and start because they aren't gameplay buttons. Heck they don't even have to be on the control panel.