Not entirely related, but do you know you can ignore blocked tiles in the campaign using game features? This was done in v1.07 I think, although I doubt it was fixed. I found the campaign to be more fun this way, anyways 
1- Design a unit with pioneer kit (pioneers aren't available in campaign, I guess to disable city creation)
2- Put a city close to the blocked tiles
3- You can now "break" blocked tiles ( I think by building, then demolishing, it has been some time since I played). This includes an overland wall, that can be found eventually
4- You can use the extended influence to teleport over it.
5- Eventually your influence can take over improvements of all other factions, even those right next to their capital.
Good luck with your cityspam!