[MFE III]

Mike, I think you'll have a problem. One, there's a good bit of power flowing through a starter switch so you'll have to be sure any switch you have is up to the rating. Two, if you're replacing the keyed ignition switch, you'll need a 3 position toggle. . . off/on/momentary on.
I'm running a keyed ignition switch and a starter button (actually two starter buttons; one on the dash and one under the hood). I can engage the starter either with the switch, or with the starter button(s) and the key in the on position.
Matt