I also want this legit, I tried to boost it and failed, but I like Artillery and plan on getting to tier X with the Russian SPG's. I've come close a few times with my fully upgraded Grille, the Grille is by far the best I've ever had, much better even than the Hummel and the splash damage seems to be the highest I've ever seen.
This is doable in any tier, you don't need to be looking for LT's to get together necessarily, in fact the best targets are TD's as they have less armour in the sides and rear. All you need is the perfect opportunity of a couple of enemies, preferably weakened right down, to get close enough, and at the same time for you to be ready to shoot, and then for your shot to hit the right place between them.
The shot itself is pure luck, but the planning for it is conscious, you need to be in the right positions on the maps. At the start of a match, watch the map, look where the enemies group and where you could get a good shot, and essentially; don't fire, at all, ever, until you have enemies close together, you don't wanna be reloading when the time is just right.
Good luck, we're gonna need a lot of it