SQL Server 2012 setup program has 2 new installation parameter
1. /UpdateEnabled:
Specify whether SQL Server setup should discover and include product updates. The valid values are True and False or 1 and 0. By default, SQL Server setup will include updates that are found.

2. /UpdateSource
Specify the location where SQL Server setup will obtain product updates. The valid values are “MU” to search Microsoft Update, a valid folder path, a relative path such as .\MyUpdates or a UNC share. By default, SQL Server setup will search Microsoft Update or a Windows Update Service through the Windows Server Update Services.

Here is sample. we saved the CU in c:\temp\sp1

Start the setup process with command line
setup /ACTION=Install /UpdateEnabled=True /UpdateSource=c:\temp\sp1

in the next setup window, setup program will search proper CU or SP automatically in the path  c:\temp\sp1.

you can select including this update or not.

If there are many CU or SP files in the updatesource path, sql server setup program will only display the latest SP+Latest CU .

you can also set UpdateSource=MU which use microsoft update service to get the product updates.you need to make sure update serve is up and firewall is setup correctly. then setup program will search Microsoft update.

This feature is helpful if you have a lot of server need to setup, you can put all service pack and CU in central place.