If you're playing hymns, play the melody as mentioned. I've tried call and response, but get no response and they look at me like what are you doing???? I also play the Flugel and try to just play harmonic progressions. If I ad lib too much, it makes the guitar player mad. Work out as much in rehearsal as possible. Ironically, because we only do "cool" music, I did sound check once and played the melody to "What A Friend We Have In Jesus" and the whole band jumped in on my sound check!!!! The FOH guy wasn't amused!!!