How to add srv record in external MS-dns server

To configure auto discovery we have configure exchange 2010 to use Dns srv record. But we are using external MS-dns how can we add the srv record.
We know that HC provide an option to automatically add the srv record but this will not help as we are not using ms-dns with HC.

You would need to add srv record in the external dns with below format
Service: _autodiscover
Protocol: _tcp
Port Number: 443
Host: mail.domain.com

for more detail consult with this kb http://support.microsoft.com/kb/940881