Setup a Rumble match on AquaDome, 1v1 and use a second controller if you have one.
Set it to unlimited time and goals.
Basically, you will need to drive around until you get the ice ball weapon, with that controller then park them in the goal area.
Using the second controller (without freeze) tap the ball towards the opposing goal.
Using car 1, freeze the ball in the goal area before it goes in.