Do you need to do that? Some foundries insist to do it in
their CAD group, not trusting the dumb customer.
See if any of the libraries (like the one with the pads in it)
has a "scribe" or "die seal" PCell? No way would any foundry
want you to free-hand it, there's a standard they want to
see and either they provide you a good cell that you can't
mess up, or they mean to do it after tape-in (just like the
density fills and other fab specific, non-circuit features).