THIS SOLUTION WILL ONLY REMAIN HERE FOR THE LENGTH OF VIRAL MONTHI've been advised against this...
In order for you to pass on this achievement, you need to have Platinum Artist.
You can pass it on, on any Multiplayer mode (Band Quickplay, Tug of War or Score Duel)
You do not need to select a character who has a platinum icon, nor do you need to select a character which you've created, nor do you need to play an instrument you didn't actually manage to pass the Endless Setlist with.
That is to say: Me, a Platinum Drummer, Guitarist and Bassist is able to pass on the achievement, if I play as a vocalist with a non-created character.
The achievement unlocks for
everyone else who doesn't already have it at the end of the song (the results screen).