Hi,

Are new site installations from multisites limited to add-on domains from the cpanel account of the site JMS is installed on?

Is there any other way around having to create an add-on domain every time. What about some type of DNS record on another cpanel's account?

(Eg, I'd like to create and install a fresh multisite slave as a demo for clients without adding on their domain as an add-on or my subdomain to get to the installation page)

Thanks,

Your question is not clear.
I suppose that you question is more relative to an automatic setup of the cPanel and not really relative to the Addon Domain or JMS.

If you want to automatically define a domain or a subdomain in cPanel, this may need that you develop something specific that can be called directly from the JMS website creation from the front-end when the "billable website" functionality is enabled.

Concerning an automatic cPanel subdomain definition, it is possible to create wildcard subdomain in cPanel.
In this case, you can define a "*.domain.com" subdomain that is assigned to a same "document root".
If you want to have specific "document root" for each cPanel subdomain then cPanel website also show how to change the default cPanel configuration to do that.
This require that you have a dedicated server and have the "root" login on your server to change the cPanel default setting and apache default module enable.
See the apache "mod_vhost_alias" documentation.

If you want that we help you doing such "cPanel wildcard" setup, this is possible with our billable support that you can order at
www.jms2win.com/en/joomla-multisite?page...35&category_id=1

Doing the same thing with a wildcard domain is not possible as you can not create an Addon Domain like "*.com".