Just for your information : No it's not possible. 
IP are addresses of computer. TCP is a connection 
protocol. To be able to talk to each other both 
computers need to use a valid, routed address.
If one don't, there is simply no connection 
possible as data will be sent to the wrong place. 
In fact the 3-way handshake to initiate the 
connection can't even happen.

The only way to use forged address for such a 
thing is to first hack another computer on the 
same local network, use it to broadcast
modified routing information and then forge the 
connection.