Your friend needs to actually read the CIC instructions on how to obtain the police certificate for Nigeria. Iit's pretty clear in saying he needs to send the application to the Commissioner of Police in Lagos, NIGERIA, not to the Nigerian embassy.
Non-Resident Requests
Applicants should apply by courier to the Commissioner of Police at the address above, to the attention of Inspector Usman Mohammed (telephone: 08033696178). Applicants should provide a pre-paid return courier envelope, a copy of their passport and a set of fingerprints taken and certified by a recognized police authority or the Nigerian embassy or consulate, and an international money order payable to the Nigerian Police Force, CID.
If he follows the actual instructions and still can't get the certificate, then he could explain that to CIC and they would probably allow for an exemption.