So by locking, I mean you can start a public match and set it to not joinable so you can play with your friends online, boost, cough*fake montages* cough lol jk


Step 1. Gather a few friends in a Xbox Live Party (Works best with 3+)
Step 2. Create a mw2 party with all members.
Step 3. Have one of your friends have the party screen up ready to invite the host.
Step 4. Have the host search for Barebones Pro
Step 5. When it says finding more players have the host only back out
Step 6. Quickly have your friend invite you back into the game
Step 7. When the host has returned, it should be on invite only. The only way people can join is via invite.

Notes:
Works almost always in Barebones FFA
Works in FFA
Not tested other game modes
In barebones, works best with 4 people total
Not tested in team deathmatch mode of barebones, only free for all