node or instance without data (for quorum)

I need to build 2 nodes of PXC between 2 data centers. In these 2 data centers, there is a public node (more important) and a private node (offline sometimes due to network issue). If there are only 2 nodes and when a node becoming offline, whole cluster will become unreachable.

In order to prevent split-brain, it should be better to build odd nodes. I want to build a extra node as a moderator to prevent this issue. But I could not build a full function node.

Is there any method to build a PXC node without data? Or any package could let a node represent only for quorum?