Easiest way to output a book project to InDesign ICML format

[cod3licious]

Description

I wanted to render my book project in the InDesign ICML format, but got a warning that this is not supported for book projects.
Is there a simple way to get the ICML output anyways, like creating a second _quarto.yml file with different specifications but still using the original markdown chapter files?
I have a graphic designer who can take care of the details, but would be great if everything was already roughly in the correct format. Unfortunately, the documentation on the InDesign ICML format is quite sparse...

[mcanouil]

Book project is a very special case. The few formats supported are in a custom/hardcoded way at the moment.

Quoting Carlos:

The implementation itself is at src/project/types/book/book.ts, but you'll see that it's really not setup well to support a new format.

Source: #6979 (reply in thread)