Hi,
Have you tried parked domains inside of cpanel?
I believe this will do what you want and allow you to have the same files on the domains which have been parked. Unless you get a wildcard or multiple domain SSL Certificate which will allow you to use more than one domain on the same SSL certificate.
You will be better off just redirecting them to the same ssl site unless you can afford one of the certificates above.
Thanks,
Trev