If you have created DJ accounts, you simply give them the same URL you use to log into your Centova panel.
www.yourcentovalogin.com:2199/login/index.phpYou could also setup a "sub-domain" on through cPanel, and created an A NAME using your Centova's IP address, and have them log in that way.
subdomain.yourwebsite.com (Set the A NAME, through Advanced DNS Editor, if your web host has it enabled).
Then they would just use their username and password you setup for them.