Quite true, why not disabling pasting on those puzzle? Hackers will still find a way, I can think of at least one, but still, most of them won't bother so much anymore.
Also, more code size/optimization games! Those ones are tough but a lot fairer.
EDIT: something to screw them even more: a watcher script that watch the input area and when onchange, doesn't allow more than one character at a time (still can be hack but it's starting to be trickier).