One other option: You can drop a marker anywhere. Touch the map, then select "Drop Marker Here". This will cause the pop-up Options marker to "stick", and this marker includes a continually updated distance.
With this approach you can select your alternative/emergency airport, drop a marker. You'll easially see the distance to that airport. And if you decide to divert, just hit the "Options" button, then "Direct to Here". It saves you from having to find the airport again.
Now, if only we had ETE on that marker!
Walter