Ok I couldn't resist looking for an existing solution - but didn't see one.

You can do something like this though:

#
# Temporarily pretends a cookie does not exist by modifying
# the HTTP_COOKIE env variable.
#
sub rm_cookie {
    my ($cgi,$name) = @_;
    my $raw = $cgi->raw_cookie;
    # Obtain a list of all cookies (they are ; separated)
    # But exclude the one with the name you specify
    my @cookies = grep {!/^$name=/} split /; ?/, $raw;
    # Replace the HTTP_COOKIE env variable with the new fake
    # set of cookies. This is important, you might not want to
    # hide all cookies - just this one.
    $ENV{HTTP_COOKIE} = join('; ',@cookies);

}
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And then if you want to remove a cookie named 'foo':

rm_cookie($cgi, 'foo');
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But keep in mind this is making perl pretend that there isn't a cookie by that name. You still need to remove the actual cookie (if this is your intent), using something similar to the parent post. Off to sleep - really this time.