Could you provide a little bit more background on what exactly your use-case is? Are the related entities that you want to tag, present in the same document/sentence, or can they be any entity from a knowledge base?
In the first case, if the entities are present in the document, have you explored the relation annotation interface that was released with 1.10? The docs are here: https://prodi.gy/docs/api-interfaces#relations. This interface allows you to annotate entities and relations between them simultaneously.
In the second case, if the entities are not in the document, I guess I'm wondering what exactly you're trying to capture? If you want to "anchor" your named entities to the real world, you could also consider doing some type of entity linking, where you would assign the unique ID Q99736 to this entity, and you'd get a lot of semantic links for free from the Wikidata knowledge base. See also projects/tutorials/nel_emerson at v3 · explosion/projects · GitHub for an example.