From L.A. you want to go north thru Santa Monica, past Malibu all the way to the Naval Station at Pt. Mugu. BEAUTIFUL ride. Stop at Neptune's Net for lunch and then on the way back there are some canyon rides you can take if you have the time. That would be my choice considering the amount of time you have.
Oh, and by the way, don't call it "the" PCH. I'ts just PCH dude!