Squirrel #10: Road to Ruin
Stop when you reach the second checkpoint, then bailout backwards into the hole in the track behind you.
Make sure your vehicle doesn't fall in as well, and a squirrel sign should be revealed.
Now respawn and continue down the track, where you will soon be knocked off again as the next squirrel appears.
Squirrel #11: Stormtrooper
After the first jump, ride to the end of the metal section of track then stop and roll backwards.
Keep rolling backwards and reversing until you reach the start of the track.
At the bottom of the hill a squirrel will appear.
Squirrel #12: Base Invader
After being launched from the ramp that moves when you land on it, bailout off the next jump with 'Bay 2' shown in the background.
Hold Y/Triangle to grab onto the winch hanging above as it moves you to the side, then release to fall onto the conveyor belt below.
This will carry you off into the factory, revealing the next squirrel in a control room.