You might also have luck with @-, brand-new to 5.6.0 (it says here in perlretut).

$-[0] is the offset of the start of the last successful 
match. $-[n] is the offset of the start of the substring 
matched by n-th subpattern, or undef if the subpattern 
did not match. 


for (qw(foo bar baz)) {
    if (/(foo)|(bar)|(baz)/) {
        print "\$+ = $+\n";
        print "\@- = " . join('/',@-) . "\n";
        print "scalar \@- = " . scalar(@-) . "\n";
    }
}
__END__

$+ = foo
@- = 0/0
scalar @- = 2
$+ = bar
@- = 0//0
scalar @- = 3
$+ = baz
@- = 0///0
scalar @- = 4
[download]

which would seem to indicate that you could do $sub[scalar(@-)-2]->();, although I think I'd prefer something easier to understand, if I were going to maintain this.