Can a domain alias be set up through Plesk?

I want to set up a domain for a new customer who's site is elsewhere, then set up a subdomain to point at it so that they can preview it before switching their domain's DNS.

So you set up...

http://www.customer.com

...in Plesk. Then set up...

http://customer.reseller.com

...which points at http://www.customer.com and can be used for previewing. Then when it goes live the subdomain can be deleted.

The only way to do this that I've found is to create the subdomain through Plesk then change the Virtual Folder of http://customer.reseller.com in IIS. This is fine for the administrator but no good for resellers or 'Clients' as they are known in Plesk-speak.

Standard Forwarding will not work as the DNS for the customer domain has not been configured yet.

Cheers, Julian