Press the [User Tools/Counter] key.
Press [Tray Paper Settings].
Press [].
Press [Printer Bypass Paper Size].
Press [Custom Size].
If a custom size is already specified, press [Change].
Press [Vertical].
Enter the vertical size using the number keys, and then press [].
Press [Horizontal].
Enter the horizontal size using the number keys, and then press [].
Press [OK] twice.
Press the [User Tools/Counter] key.