yeah, just create that user, and then set the domain stuff to be run by him.
Panel > Domain > Web then click edit across from teh domain you want the user to have access to, and set CGI to run as that user. Then when your FTP user logs in they will have the site folder right there.
The only draw back to this is that your user no longer has FTP access. You should be able to work around this, if it's an issue to you. Just search the K-Base and this forum about user dir Re-maping.