I would get confused unless someone else, such as yourself, lead the vocals since you know where they go. If you play this music track with lyrics on the screen "and" you, or someone, leads the singing, I would certainly join in and follow you.
One problem you might run into is; once the congregation joins in, the vocal leader might loose his/her place in the song due to the track being drowned out by the group singing. For this reason I would not lead the singing from a pew. I would lead from the front with the track playing in my own monitor.
If you want an instrument to lead the melody line without vocals you might try mixing in a piano where the left hand plays chords with bass and have the right hand play mostly melody. This would make it more familiar with a traditional congregation following a song lead by piano. Or, any single line melody instrument that stands out tonally or has a good amount of mid-range and up frequencies will do so long as it does not sound too much like an actual human voice. Pads and many organs would be bad. Oboe, violin, piano or electric piano might work. It has to stand out without having to make it too loud in the mix. You would have this track supporting the whole thing.
Alternately you could record yourself, or someone else on BIABs audio track or a DAW.

Does the noise in your head bother me ?