simple just /# ( # = channel number ) then just hit Ctrl + V to paste to it from clipboard just try and avoid hitting the wrong number and sending a parse to level channels like has been done many times in the past
Edit: to setup a custom channel can just right click the chat window you wish to have it show up in and then in the right side panel just makeup a random name for the channel and hit join if i remember right and make sure it is checked in the box below it