Allow users to use self install SSL cert

[Dam0]

Getting on well with Plesk, but I can't figure out how to allow customers to enable SSL on their own sites.

On my test customer, I can create a valid SSL cert but I can't select it from the "Web Hosting Settings" under Certificate. It says "Default Certificate (owned by another user)"

How can I allow my test customer to use the SSL cert installed under SMB to enable SSL on the site?

I have enabled all options for an unlimited service plan to no avail.

Thanks