Disable Chat when moderator not present

We plan to use the chat plugin for talking to a sales person. Right now, there's only one sales person, so I need a way to remove the link to the chat page if he's not logged in as a moderator. We want the button to disappear when he's not available. We also want the chat box to completely disable if he's not on, just in case they come to the page without having to click on the page.

Any ideas on how I can accomplish this? Thanks.