Well, kind of. As the OP in that topic says, in reply to that…
… and there, the answer is to basically inject an email and let the email handling code take care of it. But, that doesn’t work for this case, because I need to intervene and turn off email notifications for the user before creating the post.
It happens that we have SSO-overrides-username turned on for one side of the proposed bridge, so I think just creating something like ‘othersite-user’ could be a workaround… but that won’t necessarily work without that SSO setting.