Add a hidden-delyed node to a replica set


I have a 5 node replicaset configured with 1 Primary, 3 Secondaries and 1 Arbiter.

This is a DR setup - so I have it like this:
1 Primary and 1 Secondary in my main site
2 Secondaries and 1 arbiter in my remote DR site

If my main site goes down altogether, than one of the secondaries on the remote site will become the Primary (since there is still a magority for election on the remote site).

I need now to setup a hidden-delayed node.

My option are:

  1. Turn one of the existing secondaries to be hidden-delyed.
  2. Add another member to the relicaset and configure it as hidden-delyed.

I am not sure however which of the options will still enable a Primary election in case the main site goes down.

What is the correct way to configure this?