I think you can define your own sorting sub cmp_undef.

Something like

 
sub cmp_undef {
    my ( $a, $b ) = @_;
    return $a cmp $b 
        if defined $a and defined $b;
    return $b cmp $a; # invert order otherwise
}

@$ResultsFinal = sort \&cmp_undef(...,...),  @$ResultsFinal;
[download]

Untested!

Update:

wait this might go wrong if cmp_undef("",undef) returns 0. (Not sure)

So you'd need to treat the 3 extra cases for $a, $b being undef and return -1,0,1 accordingly.