I wasn't able to capture the alert when it happened but I was able to prompt the behavior after the fact and get these pictures. This behavior surprised me because I've never trained him to alert in this manner. I believe it's a great example of what a 'thinking dog' looks like.
Note: Bo has participated in Austin's blood sugar checks since he was a young puppy. We've always included him in the checking process. When we give him the 'let's check' command he follows us to get Austin's pack. He waits next to us as we prepare Austin's glucometer and stays with us until we validate his alert or if he didn't alert until we tell him 'all set.'