Unlock Aimee:
Complete the Bowl Ramp in Ramp Mode to unlock Aimee.

Unlock Bluebee:
Complete all Combo stages and the final stage in Combo Mode to unlock Bluebee.

Unlock Clarice:
Complete all Gawoo Attack stages and the final stage of Challenge Mode to unlock Clarice.

Unlock Grandma B.:
Complete all normal ramps to unlock Grandma B.

Unlock Mr. Honda:
Complete all Trick stages and the final stage of Challenge Mode to unlock Mr. Honda.

Unlock King Gawoo:
Complete Street Mode on Normal difficulty, and then beat King Gawoo in Street Mode on Normal difficulty to unlock King Gawoo

Use the regular controller
If you want to use the regular controller instead of the fingerboard, all you need to do is go to options and go to controller set-up and switch over to controller set up B. Now you can perform moves with the regular contol mode. It is much easier this way