WorkgoupManager is on eway of doing this (and the most sophisitcated), but there are other ways:
1) For person-by-person additions add it to ~/Library/com.apple.loginitems.plist. You could script adding this to that plist, but there are some diffuculties, namely that you need to get alias data, which is a pain in the neck. Note: copying it from one computer is not going to do what you want. The second difficulty (not as big a hurdle) is that you need to add this into the plist, and it is nested enough that you are not going to want to use the 'defaults' command, but rather need to use something more savy. I would
use Python to do it.
2) You could add this to the system-wide /Library/Preferences/loginwindow.plist dictionary, specifically as a path item in the AutoLaunchedApplicationDictionary array. This would work, and is also a GUI launcher, but it would happen for every single user. Same general issues with the plist apply as before, but you skip the Alias part.
3) If this was a more command-line based thing, then you would want to use a launch-agent from /Library/LaunchAgents. Once you get the hang of the plist format, this is the best option for non-GUI things.