Quote Originally Posted by Foz
I found this info in another thread:

Judging from this, it appears you'll need to up the conversion rates of the religious buildings, as nothing else apparently works. The only real difference is you'll need to make sure at least a basic small church is in each of your settlements. Otherwise, the idea should be exactly the same.
You could also try having a base on the walls of about 10% and giving a level 1 church an amplify level of 10 (so 10x10% = 100% converted)