I guess the song would help as long as it doesn't keep you awake while you're focusing on it. You would do it right from the beginning of the WILD, and you'd stop once the "dreamlets" start rolling in (the dreamlets being those fleeting scenes that don't last more than a second. They are there and gone before you even really have time to focus on them). I haven't successfully completed a WILD yet, so I don't know how well you can take my word for it, but I've usually just focused on my breathing while I drifted into sleep.

My problem with WILDing is that transition from external to internal focus, I pretty much fail at it consistently If you can make it work with a song, let us know!