Maintenance Mode for Transactions?

I have a request to leverage WPM for SLA monitoring.  However, the client wishes to know the uptime AND downtime in minutes. 

We need to know when the URL is in Maintenance Mode, but there doesn't seem to be a button to do so.  The URL itself is behind an F5 on a VIP, so it makes it difficult to manage on the back end.

The transaction is one step - Load page and see if "Login as..." is listed in the text of the page.

Any thoughts how to properly Maintenance Mode Transactions?