If you run Getdown with -Dsilent then it will not create a user interface for any reason.
Your question shifts polarity, you start out saying you want to "remov[e] the graphical aspects of the app" which makes me think that you *don't want* Getdown to show a UI, then you ask if there's a parameter you can pass to "have the splash show up by default" which makes me think you *want* to show a UI.
So I may be confused. But if you don't want Getdown to show a UI, you can use -Dsilent:
java -Dsilent -jar getdown.jar appdir