Relate category to multiple catalogs

We have a need for relating categories with multiple catalogs.

so we have:

Catalog1 - Code: 1

Catalog2 - Code: 2

Category3 - Code: 3

Now I want to be able to relate Category3 to both Catalog1 and Catalog2. Categories can be related to other categories just fine across catalogs, but it is the categories that exist just below the catalog that doesn't seem to be possible to relate between catalogs. Code cannot be changed, as data is coming from a PIM system.

End goal would be:

Catalog1

 - Category3

Catalog2

- Category3

Is this possible through some api I missed somewhere? IRelationsRepository cannot handle the parent of a relation being a content reference to a catalog.