Lukitoh,
IMHO you can't do it. I play melody notes by ear, but need the chords in front of me. Even with the chords in front of me, I need to know the 1st note, then I'm off. Even if I knew a song backwards, and could play it without the chords in front of me (fully memorized), I would not be able to know if a singer was singing this song 1/2 tone up or down. Well that's just me.
You want to be able to jump in WHILE the singer is singing, without hitting a couple of notes, and start accompaniment. You don't want to wait till the song is finished, its too late at that point. This is a praise & worship scenario, with the worship leader playing a new song, but one you recognize, in a new key.
Starkeeper

[This message has been edited by Starkeeper (edited 10-14-2004).]