Sima Qian created a tool that allows you to have 31 civs in a mulriplayer/hotseat game. Thread about this tool is
here. With this tool you can control any number of the civilisations (even barbarians). It also allows you to take control over an AI-civ and give AI control over "your" civ (swapping civs as much as you like). I have used this tool earlier for testing purposes, and it works fine (under Windows XP anyway - haven't tried on win7, 8 or 10).