It just occurred to me that shaneo didn't say *which* songs the instrumentalists were holding back from. It can make a difference.

I play a variety of instruments, but most often melody instruments which stand out from any group (either above or below everybody else). Which means I have to think up countermelodies.

This is no problem with a song that has a strong, definite traditional-idiom tune, like "The Lakes of Pontchartrain"; there are lots of options that add a bit extra and don't involve stealing the show from the singer.   But with most singer-songwriter stuff - Dylan and his descendants, the style where a chord progression comes first and the voice does something nondescript over it - I'm lost. Those tunes are so weak and vague that anything I could do would stand out far too much. Any reasonably competent traditional tune player can completely eclipse, dominate, gub and wipe the floor with a Dylanoid songwriter in melody composition and do it on the fly in the middle of a session with only seconds' notice, but they would't make any friends among the singers or improve the overall listener experience by doing it.