Hi PhBrand,
If you haven't gotten any responses from other customers or Support people yet, then this may be because of the complexity and overhead involved in getting that scenario to work. I suspect it's quite possible, but it would be a very involved discussion with many details and would likely require some environmental configuration changes outside of the officially supported (QA'd) use-cases.
At this point, given the complexity of the project and uniqueness to this scenario, I recommend getting in touch with your CA Account Executive or CA Sales and inquire with them about hiring CA Services for this type of project work, as these types of projects are what CA Services specializes in.
But at an extremely high level, my initial thoughts are that this may be possible with the right use of both database replication and file system replication, and likely some environmental configurations outside of the Portal and Gateway nodes. I'm sure there is a lot more to it than just those three items though, and this is where CA Services can come in and assist.
I hope that helps at least point you in the right direction, even if it's not all that useful.
Sincerely,
Dustin Dauncey
Sr Support Engineer, Global Customer Success
Email: Dustin.Dauncey@ca.com
Phone: +1 800 225 5224 ,48385
Phone if outside North America - https://tinyurl.com/CAContactSupport
CA API Management Community: https://tinyurl.com/CAAPIMCommunity