What the hell is wrong with saying, "I learned this song from ... " ? Before my voice turned to a croak and my fingers started numbing out, that was good enough for me. "Source singer" just has a kinda chi-chi tone to me, though objectively there's nothing wrong with it and I don't see it as demeaning the source. Maybe it depends on the tone of voice in which it's spoken?

And if you're singing "The Death of Mother Jones" (it has been done), Gene Autry damn sure is a "source singer." Not to mention a couple of dirty old hokum numbers I used to do just for the pleasure of saying, "I learned this song from a Gene Autry record." Oh you can feel-a my leg, you can feel-a my thigh/But if ya feel my leg ya gotta ride me high ...