If they have their MEI you should be able to log it as PIC/Dual received assuming you have your Multi. Think of it like you are instructing a student in an Arrow. They log it as PIC (because they are rated in single engine airplanes) and they still log time under the "Complex" column if they want. You can't ACT as PIC, but in this case I would think you can LOG PIC.
If i'm wrong someone please correct me...