OK, I've got a couple of ideas. I've tried to list these in a way that they could be used to aid Open/Conquest as well as hinder Predator.
- Remove/Add traits
- Reduce/Increase starting gold
- Add/Remove starting units
- Add/Remove initial starting techs
- Change individual player difficulty (not sure what this does, but in the editor you can change the difficulty level for player 1 independently of the others. Maybe this can be used to change Player 1's production level?)
- Render some of the tiles around the start location unusable via pollution (for Predator)
- Add some roads around the start (for Open/Conquest)