Mithun's last post in particular.
As it stands, if you don't want to use the SEPM's Deployment and Migration Wizard, nor the GPO method, then you're probably looking at using Altiris and the SEP Integration Component.
http://www.symantec.com/business/support/index?page=landing&key=56176
This will allow you to automatically discover and install SEP to computers on your network and/or domain. In additiona to this, the SEP Integration Component is also able to auto-magically remove McAfee before installing SEP as part of the same process, minimising the time your endpoints sit there without AV.
The only downside is that you need to setup a (temporary) Altiris server to do this. It's not a native part of the SEPM install. Then there's the fun in going learning to use it, which can be take a little while. It also uses its own separate agent to manage the SEP installation on your endpoints.
The tool itself is great for ensuring automated coverage across your managed devices, just make sure you have the time to get your head around Altiris first if you're not already familiar with it.