The CHYOO2 software does not usually allow more than four options to be added to a thread, but this trick allows a fifth to be added. There is no limit to the number of extra threads that can be added this way.
Go to the story map and find the thread you want to add a fifth option to. Click on it to open it. You should see in your address bar something like
Notice the two five-digit numbers at the end. Make a note of the first set of five digits (ie. the "12345" in our example). Now find a thread in another story that you can add a new option to, and hit "Add new thread". You will see in your address bar something like
Replace the five-digit number at the end with the one you made a note of. Copy this entire address and open a new window with it. You are now adding a new option to the thread you want. You can tell it's working if you see the continuing question for the intended thread above the edit window. Write the thread you want and submit it normally.