You purchase missionaries and they go really out of the way to find barbs. And then when you find them, it's a long trek back (if that's where they want to go). My last game with HC was just awful, but I can see the promise. You can CS gift the trash units immediately, maybe combining with Freedom. I converted a captured settler, which REMAINED A SETTLER. Settled Uluru on the other side of the world with it. Converted lots of navy, which otherwise I would have to hard build and they move fast. The CS accept triremes and galleys as gifts. Sent tons of gatlings to help my faraway CS allies (but not gift them). Gunboat diplomacy.
Best AI exploit was, I stationed brutes and archers on the archaeological sites, which frustrated the AI archaeologists. But guess what the AI does: they KEEP BUILDING THEM. I DOWed a couple AI and captured 11 archaeologists, and ran out of museum slots so fast I had to start annexing cities.