Curent class .dropdown-submenu > .dropdown-menu have left: 100%;. So, if you want to open submenu on the left side, override those settings to negative left position. For example left: -95%;. Now you will get submenu on the left side, and you can tweak other settings to get perfect preview.
EDIT 2: Demos aren't working, because Bootstrap changed their URL's. Just change external resources in jsfiddle and replace them with new ones.
Thanks. Almost exactly what I need, however, there should be left: -90%; (otherwize I can't move my mouse to that submenu, cause it disappears).
Like i said, that is just idea what you need to do. Glad i'm helped :)
none of the demos are working
none of the demos are working for me either