In order to do this you will need to create a new admin group within the center:
  1. Login to the specific center
  2. Create a new group
  3. Set Security mode to Admin Security Group
  4. Set the Security category to the center
  5. Set the group type to Sub-Administrator or whatever is preferred
  6. Save group
  7. Edit Permissions
  8. Merchant Account Management - Manage Merchant Account
  9. System Administration - Super Administrator
As long as the admins that are added to the group are only set with access to a particular center, the "site admin" access will not go beyond that center.