Here are two of the harder to find mini-games. At the College, find the green transformer next to Billy's Sporting Goods and do a lip trick on it. Then quickly grind the flashing wires to bring the voltage back down to zero. It's hard to find but the transformer is on the ground with a really small pipe hooked to it.

At the San Franciso pier, go straight to the ocean, to the big bowl there. You will see two telescopes between two different quarter pipes. Look through the one on the left for the mini-game.