'Inscribed in the book of life' about a dead person

I've seen "may his name be inscribed in the Book of Life" used as a condolence a few times. Is this an OK usage? I have only used the phrase on the High Holidays to say "May you be inscribed..." and it doesn't make sense to me to say it about a dead person.

Thank you for your question,
there is no source for this custom, however, there is no prohibition in saying it.