Here, this is in response to another one of XBL Junky's attempts to sell this guide
Posted in another site -
Go into a custom game lobby.
Click 'A' on second controller. Do not click yes.
Hit 'B' twice on your main controller.
Click 'Use Temporary Profile' on second controller.
You should have a window pop up that gives you the option yes or no
Join someones game through the guide button
When the "Joining in Session Progress" window pops up, hit the guide button again
You should be in someone else's game while still being on your mini dashboard.
Have him/her start matchmaking and when you guys get matched up with other people, hit the guide button to close the mini dashboard
Then, click yes and change your sensitivity.
Then you have whatever random name you end up with in the H3 Temporary Profile Names Box
This is in response to that r-tards topic to sell this tutorial.