DS 7.x removed the ability to use the Boot Disk Creator (now called BootWiz) directly for managed automation environments. BootWiz was the only supported way to modify the HOST files in previous releases, and so far there is no exposure in the SMP Console to add entries. Since the HOSTS file for Linux and WinPE automation is generated on-the-fly by BootWiz, you can't simply place a file in the folder structure and make it be "used" in automation.
The only way to get a HOSTS file in automation therefore is to modify the Default.BDC file, or Boot Disk Configuration file. This file is essentially an INI file read by Bootwiz during it's build process behind-the-scenes. Adding various sections and entries to this file will modify the way the automation environment is generated. For instance, you can include certain things into WinPE, or create custom entries for HOSTS files.
For this specific issue, a section needs to be added similar to the one that follows. This particular section would include a host entry for both the short name and the FQDN of the NS called "myserver."
There are multiple places where you may make this change. There is a hierarchy used by BootWiz to read configuration files, starting from the top location below to the bottom. Each layer read, by default, over-writes the previous layer if there is overlap, and inherits the previous layer where there is no overlap. Thus, you may want to make a change at the top layer that is universal, and then at the bottom layer you could build an individual file that is specialized for one particular environment. Each of the following locations will have a "." representing a base location for the task handler location where bootwiz resides. This is either \\yourserver\deployment\task handler or "c:\program files\altiris\altiris agent\agents\deployment\task handler".