Propagate entries manually between sites

I have a client that wants to setup a multilingual site, but for the purpose of this site they only want certain entries to be translated.

If I setup sites that use a section which is configured to NOT propagate entries across sites, then I haven’t found a way to link entries manually for entries that I DO want to propagate. Is this not possible? One could of course just create the entries manually, but then I loose the linking between them to provide a language switcher though. Also, I can’t really re-save an entry on another site easily.

Is the preferred approach to do propagate and keep them unpublished? I feel that that makes it unwieldy very quickly…