I just wrote a new web page with ideas for choirs who don't have any instrument player. Check it out: 3 Ways a Church Choir Can Minister When They Don't Have a Musician. The page talks about three strategies -- singing a cappella songs, using instrumental tracks, and doing songs that are so very easy to play that someone in your church could probably learn it even if they haven't ever played before.
To go with that, I've written a page with step-by-step instructions for how to play one very easy song. The page is called "Gospel Music for Non-Musicians: You Can Play 'Holy Spirit' by the New Jersey Mass Choir".