Oh, no, dammit, I haven’t. Doing that just shifted it to be under the title of the song itself.
Finally cracked this one. By fishing around this forum, I found instructions on how to import the .scrformat file Title Options Example.scrformat:
Go to Compile, then at the bottom of the Formats pane on the left there’s a gear icon; click on Import Formats, navigate to where the Extras Pack/Title Options Example.scrformat file is and import it. Add it to My Formats.
This adds a Section Layouts “Section Title” item called Song Lyrics with the title expressed as:
Section Title
By Singer
Choosing that allows you to set Custom Metadata (in the project, in the Inspector) called Singer and set that for each document, so if you want a song to be “By Fats Waller” you type in “Fats Waller” under that Custom Metadata you’ve set up.
If you don’t want the Singer name, choose the Section Layout/Section Title item with just the title.
(This “By Singer” Section Title would also be useful if there were a version with By Author - but I suppose you could call the option Singer but use author names, for instance in a collection of short stories or academic studies.)
I still have one question: how do I take my own name off the ebook as author? I’ve taken my name of of the metadata, but it stubbornly appears on the ‘cover page’ generated by the project when it opens in iBooks.
Edit: cracked this too, in a way - the author name is greyed out and Scrivener seems to automatically choose the name you bought the program under. If you enter a different name in the Authors field (Compile, choose a format, and over on the right the second-left icon in the series of labels - the one that actually looks like a label), it’ll use that.