I would also very much like to be able to do this.
I work for a global company so a lot of the posts that I put on our social channels are to a segmented audience (language/location). Currently Hubspot does not have the functionality to do this, so I have to schedule my posts in other platforms. However frequently these posts are part of a wider campaign and so I would like them to be attributed to their campaign on Hubspot. The posts do pull through to Hubspot once they are live, so I can see them in reporting, I am just not able to add them to a campaign.