Specify SNI for Website Checks

I have an Azure Website that is used by our company when our primary website goes down. We call it our DR website. This is done automatically using Traffic Manager. 99% of the time, our main domain points at our real website (I'm already monitoring this).

I want to be able to monitor this Azure DR website's certificate to ensure we're alerted when it expires. However because 99% of the time our domain points to our real website and not the DR website, I need to use the DR website's IP for the check.

This adds a new problem in that Azure websites share IPs between customers, and use SNI to determine which customer to route traffic to. LogicMonitor's website checks don't provide a way to specify the SNI header. I've tried setting the Host header to our website's domain but that didn't work.