I agree with @NigelG - this is quite tricky to do on the fly. Depending on how you source the original lists, you could, as I think he’s alluding to, iterate through the account Ids and create each of the regions for them. You would indeed do this using an API workflow.
EDIT: I’ve made a change that seems to resolve the ordering issue.
By the way, I feel like there might be a way to use nested RGs for this but I can’t quite figure it out and I’ve run out of time. Just throwing it out there, again, in case it sparks an idea for someone else.