I think it depends on how many participate in the sing along..

If there is a great interest and participation, you can wing it...

I think about the Xmas show I do for my daughter's class (she is the teacher)..Children and parents all join in... informal, and great results... they have a good time... and easy to play on arranger like the EA7..

If the sing along material is as easy to perform, it could be a great "winging it" gig..

Remember the poster asked about the Projector, and why the response was directed towards his question