If you have a Server 2012 Host not part of your LAB and you wish to have security essentials installed until you have ConfigMgr up and running this can be done as outlined below:

NOTE* – Microsoft Security Essentials is designed for Windows 7 and is not compatible (nor supported) on Windows Server 2012.

But if you insist, you might as well end-up installing it on your Windows Server 2012.
1.Download a copy of MSE from Microsoft
2.Right Click on the “mseinstall.exe”.
3.Click on Properties.
4.Click on the “Compatibility”-tab.
5.Locate the “Compatibility mode”-section.
6.Check “Run this program in compatibility mode for:”.
7.Select From the (now active) dropdown menu “Windows 7″.
8.Open a Command Prompt as Administrator.
9.cd to your Downloads folder (ie. cd C:\Users\%username%\Downloads).
10.Run “mseinstall /disableoslimit” and follow the installer prompts to install MSE on your Windows Server 2012.