no such thing. You have to broadcast some sort of IP if you want the data to return.
You can proxy or relay connections and possibly spoof if you are in a linux/unix environment.
Umm... there is such a thing, unfortunately they mostly suck and on top of that they want to charge you $30+ for they're crappy software.
Let me explain what I want to use it for and maybe it will make a little bit more sense. Baseball has a site MLB.tv that allows you to watch baseball games online for a monthly fee. Unfortunately blackout rules apply so you can't watch local games even if they are away. The way they determine where you are from (and wether you should be blocked) is by looking up your IP. What I would like to do is mask my IP and make it seem that my IP is coming from another location that way the game would be visible to me.
I was able to do this with a few utilities I found using Google search, but none of the ones I used were reliable and the majority slowed down the connection to the point where the video was constantly buffering. I am sure there is something out there cheap/free and easy to setup that will do this for me, but I haven't been able to find it. If someone knows, post up. TIA.