As much as I cannot script, Blizz makes a point. There might be some kind of terrain tags somewhere that displays message but most likely not. Of course, calling a common even and copy and pasting on every troop wouldn't be too time consuming. Even Blizzards demo has around 40 troops (I hacked it, not for cheating, for reference O-O), setting the common even to a copy and paste would make adding it as easy as click on eventing troops add-on and hiting the nifty Ctrl+V button and moving on. Takes about 5 seconds on each troop..
But, possibly go for Blizz's technique. And maybe if you ask nicely, make a shrine of him in Toronto, pray to him and give him bribes he might script it for you. Okay, maybe if you ask nicely. It seems like a small script, still to big for my understanding. Makes me wish there was a 'RGSS For Dummies' eh?