I've found one of the best "solutions" is to delay the arrival of the mid-game. You do that by expanding slower, and using the console to help the Eleutheroi, which stops any of the other AI factions growing too powerful, too quickly. Don't let any AI factions die, because once that starts to happen, you get a snowball effect to a handful of unstoppable superpowers. I add money to the Eleutheroi via the console a lot at the beginning (you can tell if you've overdone it, because they start making huge pirate fleets), and I also add troops to the garrisons of significant places. If someone starts steamrollering their local rivals, I'll use Force Diplomacy to take settlements off them and give them to the weaker faction. Or create new migrated areas like Galatia or Bastarndolandam to add extra chaos in a region.
Now there is a hurdle in all of this; after about 230BC the Eleutheroi FMs who are governors start to die off, making them much easier targets (given the way autocalc works). That means you need a fairly active monitoring of what's going on, but it doesn't add much overhead really.
For the results, look at the minimap in 239BC in my Epeiros-as-the-Bosporan-Kingdom game:
Every faction is still in existence, there's still lots of rebel territory, the Romans aren't already in Gallia.