I don't know the significance of the PERLIO environment variable but I can suggest a work-around to getting the environment variable set if isn't already: re-exec the current program after having set the variable. You could put this code into the import() function of a module and say use ... ( PERLIO => '...' ); if you needed/wanted to abstract it out.

BEGIN
{
    if ( not $ENV{'PERLIO'} )
    {
        $ENV{'PERLIO'} = ...;

        EXEC_LOOP:
        {
            exec $^X, @ARGV;

            # This should not be reached.
            warn "Couldn't fork: $!";
            sleep $sleep;
            redo;
        }
    }
}
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