The subject for the certificate used on pop.gmail.com:995 is
subject=/C=US/ST=California/L=Mountain View/O=Google Inc/CN=pop.gmail.com
There is nothing you can do to change that. If you are accessing pop.gmail.com using any other name, a client will display a certificate error.
If Google wanted to allow you to use a different name, they would have to allow you to supply your own certificate, and they would have to come up with an IP address or port that is unique to you. As far as I know they do not support this.
Of course you could also disable certificate warnings in your mail client, but that would be a very bad idea from a security stand point. You probably just need to accept that you must use