IF you make a custom game you can invite friends there will be an option to invite them. Otherwise press the playstation button in a custom game creation and go to their names and press triangle and up the top should be INVITE option.
You may run into some problems though some people seem to get D/C. From my experience i have invited someone and started a game and they seem to join fine when i am in the match. Sometimes being in a party causes the game to d/c or not even work.