Perhaps a simple check of their code for the offending variables, and then either reject them, or run them via a system() call to a seperate Perl process. At least that way a single use of the variables wont affect the entire body of code.

Unfortunately the problem here is that if the engineers are crafty it will be nearly impossible to prevent them from using these vars or for detecting when they have done so.

Which means that in the end Abigail is correct. The best way to resolve this problem is to train the engineers not to use them.