I don't really have an issue with the mouse (or ending dialogues in general). But if there's a key needed, the best bet would the be the very last of the keyboard, and simply giving what would now sometimes be 7 or 2 or 4 all that number (0).
Personally I find it very unneeded, but apparently people want it, and I think that's a better resolution than escape or an entirely different buttom than the 1-0 keys.