Is there any way to add additional passive rack elements, like a fiber patch panel for example. Would be great to be able to add these to make the system image resemble the rack as much as possible.
Not yet implemented, you can follow this issue to see when it will be: https://track.radensolutions.com/issue/NX-2114
For now you can create a chassis, give it a custom image and place in the rack. The only downside is that it will have Unknown status.