Once upon a time this technique was blessed and documented by Apple
The technique used to replace the Finder is discussed in detail in the
Replacing the Finder section of Inside Mac OS X: System Overview.
A installer can programatically replace the Finder by calling system
and then the defaults command-line tool using the techniques described in
System Overview.
(While "Inside Mac OS X: System Overview" is no longer available it used to say "defaults write loginwindow Finder path" which come Snow Leopard was nixed)
What you can do atm is compile a applescript to quit finder so it does not relaunch and add both that script and terminal as startup items, it is not that pretty but it works.
echo tell app \"Finder\" to quit | osacompile -o /Applications/Utilities/QuitFinder.app
defaults write ~/Library/Preferences/loginwindow AutoLaunchedApplicationDictionary -array-add '{ "Path" = "/Applications/Utilities/QuitFinder.app"; "Hide" = "1"; }'
defaults write ~/Library/Preferences/loginwindow AutoLaunchedApplicationDictionary -array-add '{ "Path" = "/Applications/Utilities/Terminal.app"; "Hide" = "0"; }'