I don't think 'excessive overhead' has any meaning without a context. It might be excessive for some applications and not for others.

And I think the interface is sufficiently interesting that the overhead might be worth spending. Being able to write

    $stack = newitem;
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for a push operation and

    $top = $stack;
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for a pop operation is pretty clever.

But one thing I would do differently is to resolve the fifo/lifo string to boolean in the TIESCALAR method instead of doing it over and over on every FETCH. Just change the TIESCALAR like this:

sub TIESCALAR {
    return unless $_[1] =~ /[fl]i[fl]o/i;
    my $stack = $_[1] =~ /([fl])i\1o/i;
)   return bless [$stack,[]], $_[0];
}
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Then we can eliminate the regex from FETCH; the if line becomes simply:

    if ($_[0]->[0]) {
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