Well, WA can display it -- the challenge comes from the fact that there is no way to get an accurate distance out of the WoW API for an enemy target like that.
You can estimate it based on items, or spells, that have a known range, and figure out which ones are in or out of range. (Don't need the items even.)
That is probably most easily done using librangecheck or some similar library, along with your custom trigger in WA.