return_to_channel = UCXF
CFG should create a config.txt file when you select "save" from one of the settings menu's. If not just create one with notepad and place it in the apps\USBloader folder.
Here is a link which shows other options which can be set in the config.txt file.
This is the contents of my config.txt file with comments in brackets (don't include the comments in the config.txt file)
device = usb (sets cfg to look for games on the hdd)
gui = start (sets cfg to launch in gui mode)
gui_style = carousel (sets the gui style)
covers_path = usb:/apps/USBLoader/covers (these covers_path settings define where cfg stores images, this line defines where the image cache is kept)
covers_path_2d = usb:/apps/USBLoader/covers/2d (2d images)
covers_path_3d = usb:/apps/USBLoader/covers/3d (3d images)
covers_path_disc = usb:/apps/USBLoader/covers/disc (disc images)
covers_path_full = usb:/apps/USBLoader/covers/full (hd images)
return_to_channel = UCXF (returns wii to cfg when exiting a game)
fat_install_dir = 2 (defines naming convention used for wbfs files when backing up a disc through cfg)
Hope this helps.