If you can't get people to read the module documentation, I don't think there is a way that you can prevent people from finding old versions of XML::Simple for their use.
I think the best approach you can do is to write good articles on how to use solutions other than XML::Simple. There have been many times some solution has been recognized as bad, either by some or by many people active in a part of the Perl community. Not all these drives for excising a practice have been beneficial looking back, for example the Perl Best Practices and the Inside Out Objects technique to bring up some older examples. I don't think that it is easy to reach the people who need your advice the most, and the best thing you can do is to make it easy to do the right thing instead of making it hard(er) to do the wrong thing.