Requirements:
Laptop, Router, and Bandwidth Manager program

LONG and DESCRIPTIVE Tutorial:
This is a very noobish and old technique, but clearly works. You do NOT have to be host, just simply in a lobby of which you desire. Once in said lobby use your laptop to pull bandwidth from your network. Depending on which program you decide to use will dictate what percentage of data you should flood your router. With my untold program I decrease my Xbox's bandwidth to half a kilobyte. Once all have "Left" your lobby deactivate your program. Your program will dictate the method of which you use to lag yourself out of the lobby without lagging yourself off Xbox Live, which in turn will cause you to lose the lobby all together. If ANYONE needs help on figuring out what program to use, feel free to message me, but keep in mind I will NOT supply nor condone any piracy as most efficient programs require money.

Brief Tutorial:
Enter desired lobby
Activate program
*Everyone Disappears*
Deactivate program
You are now HOST

Its as simple as that.

NOTE: Flooding or limiting your Xbox for too long of a period of time WILL lag you out of XBOX Live forfeiting the lobby you're attempting to duplicate. (Mentioned TWICE now)

NOTE2: Disconnecting ethernet from the xbox will not work.

NOTE3: Disconnecting ethernet from modem will not work (Modem-Router) (Internet SOURCE)

If NOTE2 or NOTE3 DO work... muh bad for the misleading information. Try at your own risk... fear of losing one's character can sometimes find in itself to be quite devastating for many.