Yes, might be possible.
But I thing exactly the honor system would be responsible, that members who really go out for a cache and find the individual code in that special cache, would not tell it to a friend or someone who will post it somewhere.
So if you would try to fake a log, it would be much more difficult to a) get the right code from the corresponding log book and b ) if you got it from somewhere, it would take more time to log. These two facts could cause that fake logs for more than hundreds or thousands will become uninteresting.
Look at here, it is just a sample: http://coord.info/PR54VE6
No honor, just fake!
Napalmrocks