Insurance companies have a very good reason for refusing to do this, as you've already noted.
Don't name him as an additional insured. Renter's insurance is for the CONTENTS of your apartment and for things that happen in your apartment (someone slips and falls). It has nothing at all to do with the apartment itself, which your landlord should have incured.
You don't want your landlord to have a claim on the reimbursement for YOUR stuff if something should happen to the apartment.
There's a good article about renter's insurance here.

