Can't use a former appleID email as my custom domain for iCloud email
I'm trying to set up a custom domain for my iCloud account. My wife once used her real custom email address as an Apple ID. I deleted that Apple ID about a year ago. But when I try to add that email address (that I own) in step 2 of the custom domains setup it says I can't because it is being used as an Apple ID.
This seems absurd. To block using an email address just because it was part of a long deleted Apple ID.
Does anyone know of a way around this? Without being able to use my wife's actual email address it basically makes the entire custom domain setup pointless.