Do not try to create a global/master ftp using Plesk, this is a massive security no no as it uses the standard FTP port.
Install Filezilla Server
Configure Filezilla Server to run on another port that is not commonly used by another service (i.e. not 21,25,80, etc)
Create a user account in Filezilla that has C:\inetpub\vhosts as it's home directory.
You now have a global ftp account.