Why would he want to log SIC when he could log PIC.
If the Capt is an MEI and willing to sign a logbook, your student can log it up. This is not only legal dual recieved, I also think it would be ethical as well. Assuming the capt has more than 200 total, there is a TON your student could learn from him.
In my mind, if he's not required, but is gaining experience, he is receiving dual. If he's receiving dual and he's a multi-comm, its PIC. PERIOD.
Also, just for the record, I agree that you should try to convince him that he's not going to go anywhere with 1000 turbine-PIC dual received, and that he has a lot greater chance of not killing himself or others in the future if he gets into a better career path to learn...ie, CFI, night frieght, etc.