This is a slightly silly thing that I've recently been surprised to discover actually works...

{
    package String;
    use base 'CORE';
    use overload
        q[bool]   => '_deref',
        q[""]     => '_deref',
        q[0+]     => '_deref',
        fallback  => 1,
    ;
    sub new {
        my ($class, $str) = @_;
        bless \$str => $class;
    }
    sub _deref {
        ${$_[0]};
    }
}

my $greeting = String->new("Hello World\n");
print $greeting->substr(6);
[download]

It's not really obfuscated, but even experienced Perl programmers would probably do a double-take when seeing it, and I couldn't think of a better section to put it in.

By the way, you can also use CORE directly - the subclassing is not strictly necessary.