I offer the following policy as an example of how this was handled in one of our Circles. I am curious to hear feedback from the Community.
Policy: Key User Role Representation
It is a policy of this circle that individuals assigned to the Business Process Owner role shall also be assigned to the Key Users role and that, further, such individuals shall represent both the Business Process Owner role and the Key Users role in all circle meetings. Key Users who are not also in the Business Process Owner role shall not be considered core circle members.