Make a zip folder, place it within the folder structure that you push to the marketplace.
I would place it in the same folder as the mesh. The editor won’t show the file(s) anyway, since they aren’t editor files.
There are no rules against this / the guidelines have been amended and make no direct mention of similar cases.
I would make sure to label the zip folder appropriately, and submit for approval to see if they flag it. They probably will.
Simply communicate with the person assigned to the review to ask where to include it / how.
Being those aren’t engine files it may require some work-around.