I think that it is possible, because in the mapping really (physically in the storage model) you have the foreign key imported in to Employee referred to the Person ID.
Try to create a 0...1 --> 1 association from Employee to Employee
in Mapping Details:
Maps to EEmployee
- EEmployee ID Person <--> ManagerID
- EEmployee1 ID Person <--> ID (that is the foreign ID of Person contains in Employee table)