My and my friend Erazor found this super easy method to get this. It does require you to coop it, but it will only take about 10 minutes for both people if you do it this way!
1. Get into the same party in game
2. Make a Custom 1v1 Strongholds match with these settings:
As many helpful skull as you can find.
No Fog of War.
3. Once the game starts, split the Strongholds between you two leaving ONE stronghold uncaptured!! Thanks WhitePrinceLion, he and a buddy discovered that the game goes into Sudden Death if the 7th stronghold has not been captured and the strongholds are 3 each!
4. Delete any buildings other than barracks and rebuild barracks on the closest stronghold to #5.
5. Choose a nice large area on the map where you can gather a LOT of troops in one place and place your global rally point there(hold
6. Spam suicide grunts!
7. Once the other person has enough or maxed the grunts there, use the Glassing Beam/Superpower to annihilate the grunts.
8. Alternate the leader powers--the dropships ability will count assuming you have population room for it, and the mines help a little as well.
9. Just wait for the leader powers to recharge and blast them again! It's really fun actually.