Micaelis Rex
Prince
OK, I just thought this up, it seems brilliant, atleast on paper. 
As soon as Poly is a turn away from taking Catchopolis, we go to GCA, and ask for peace. In exchange for peace, they must gift us the chokepoint city. This will block off Poly and give GCA's final city or two protection from that huge Poly army. We stock the chokepoint city with about 5 veteran pikemen, to seal the deal.
To get Poly's approval for this plan, we promise them 4 things, and they promise us 1 thing. One, they can have all of GCA's territory east of the chokepoint city. Two, they can have most of the undeveloped northern land. Three, we promise to take out the final GCA city, to fulfill the deal with CDG. Finally, we promise to vote for them in the UN, assuring their victory since there will only be 3 civs left alive at that point. Poly agrees not to attack us for the duration of the game so long as we don't cross the borders that will be set by this treaty. This will give us much needed security.
Yes, this will severly limit our empire, giving them a bigger one, but reality is that we aren't giving them anything they don't already have. We cannot settle the northern area as fast as them, and even if we get a city or two down, we couldn't defend them. Instead, let us defend our cities well, and prepare for the endgame.
Our hopes for victory is to build a spaceship, which is a possibility if we can stay even on tech to Poly and CGN/GWT. We have some nice land, which will eventually produce nicely for us, so a spaceship victory isn't that far-fetched.
Now if we don't do this, we will get less land as Poly will get the chokepoint city, and will eventually attack us to give them a powerful enough base to out research GWT/CGN to a spaceship finish. Of course this will not happen tomorrow, but it will happen eventually.

As soon as Poly is a turn away from taking Catchopolis, we go to GCA, and ask for peace. In exchange for peace, they must gift us the chokepoint city. This will block off Poly and give GCA's final city or two protection from that huge Poly army. We stock the chokepoint city with about 5 veteran pikemen, to seal the deal.
To get Poly's approval for this plan, we promise them 4 things, and they promise us 1 thing. One, they can have all of GCA's territory east of the chokepoint city. Two, they can have most of the undeveloped northern land. Three, we promise to take out the final GCA city, to fulfill the deal with CDG. Finally, we promise to vote for them in the UN, assuring their victory since there will only be 3 civs left alive at that point. Poly agrees not to attack us for the duration of the game so long as we don't cross the borders that will be set by this treaty. This will give us much needed security.
Yes, this will severly limit our empire, giving them a bigger one, but reality is that we aren't giving them anything they don't already have. We cannot settle the northern area as fast as them, and even if we get a city or two down, we couldn't defend them. Instead, let us defend our cities well, and prepare for the endgame.
Our hopes for victory is to build a spaceship, which is a possibility if we can stay even on tech to Poly and CGN/GWT. We have some nice land, which will eventually produce nicely for us, so a spaceship victory isn't that far-fetched.
Now if we don't do this, we will get less land as Poly will get the chokepoint city, and will eventually attack us to give them a powerful enough base to out research GWT/CGN to a spaceship finish. Of course this will not happen tomorrow, but it will happen eventually.