I think he means with "without copying etc.", that you currently can't say (like Sketch) "insert > symbols > symbol x". If you want to use a symbol now, you'll have to search through your design and find where it is used (which can be hard with overrides) and copy that one to re-use it.

Workaround would be to keep all your masters organised on a single page, but (here we go) you can't share between documents yet :)