We had a client request this and we said no.  I forget who explaind it this way (might have been our insurance agent) but they pointed out that the request really doesn't make any sense, why and how could a beneficiary of a potential payout also be an 'additional insured'?

I am way out of my depth with the explaination here - I just remember that we were advised on this question and we did refuse without any real consequence or negative reaction by the client.