Removing an activity from the history stack

My app shows a signup activity the first time the user runs the app, looks like:

1. ActivitySplashScreen (welcome to game, sign up for an account?)
2. ActivitySplashScreenSignUp (great, fill in this info)
3. ActivityGameMain (main game screen)

so the activities launch each other in exactly that order, when the user clicks through a button on each screen.

When the user goes from activity #2 to #3, is it possible to wipe #1 and #2 off the history stack completely? I’d like it so that if the user is at #3, and hits the back button, they just go to the homescreen, instead of back to the splash screen.

I think I can accomplish this with tasks (ie. start a new task on #3) but wanted to see if there was simpler method,

Thanks