It'll help explain how the add-on feature works in Cpanel, basically it edits the Apache config and makes an additional in the available sites folder that looks for the referring domain name i.e the A record. Now your host allows you could add this manually but this would be the same as using the ADDON feature, but you need to inform your server about the referring domain via the config and without this it doesn't know what Virtual Folder to use, so if you do point it.. chances are it will just return unavailable or ABC.com site is accessible though DEF.com because it they are on the same IP and ABC is the default site.
Can't be Done Sorry
So in other-words, no you need to use ADDON - that's how you add additional domains to cpanel accounts unless you have a multiple user cpanel account in which you just add another cpanel account and then add the domain as the main site for that account.