How do I create a right column when I have a 2-rows layout? Suppose I have 2 windows under the following layout:

 _____
|_____|
|_____|


How do I create a right window so that it becomes:

_________
|_____| |
|_____|_|


Without disturbing the open ones?
Split the two editors separately, but make sure the splits align vertically:



Note that once the vertical splits are aligned, they become locked.

I actually wrote a feature request on the wiki a while ago asking to improve this behavior.