Just...
No one ever asked for Bliss. For anything. Ever. Anywhere. He picked an absurd choice like that on purpose.
A solution to his little problem there? Make the book about Mercury and ...other character...AND Icarus coming back. Maybe they're tied to the thing that brings him back or are part of the team that's there when he comes back. Honestly there's ways to do things they just require some effort and thought.
And "They're not as popular as this other character" is a dumb cop out reason not to use characters.