This option still works for Opera 29, I recently used this myself. And I also see where you're going wrong:
Alt-P (open settings), don't click anywhere, then use: Up, Up, Down, Down, Left, Right, Left, Right, b, a.
So instead of using up/down a few times you need up/up, down/down. The option you're looking for can be found further down on the same page (after you enabled power user mode of course).
Hope this helps!