1. ****
I will look further if it is possible.
2. *****
So basically what you are saying, that there is not even possible if install additional exchange server in a roll of hybrid server, with different url.
So Basically, I would have to do cutover Exchange migrate. And then implement ADFS and Dirsync for that organization mailboxes. I will have plenty of downtime, when switching to SSO.
Thank you