So you can easily recreate this behaviour yourself by doing this on launch.
-(void)applicationDidFinishLaunching:(NSNotification *)aNotification{
if (([NSEvent modifierFlags] & NSAlternateKeyMask) != 0){
//holding down option on launch
//Do the optional path stuff
} else {
Dear list,
I remember seeing the functionality in some apps where one can hold the option
key while launching an app to allow the user to choose which app data store to
launch. So is this a core-data app functionality that's already built in to the
frameworks, or does one need to implement that