Repackaging Installer that creates a global login item?

I have an application that I'm working with. It's already distributed by the vendor as an installer package, which is great. However, the tricky part is that in the postinstall for the package, it calls one of the programs that gets installed with a -install flag, which in turn adds a "global login item" (an "AutoLaunchedApplicationDictionary" entry within /Library/Preferences/loginwindow.plist) on the startup disk, not the target disk. Any suggestions for handling this?