Do I Need Shorter Cranks?

My bike is a Cervelo P2C with 175 mm cranks. I'm 5' 10" with an inseam of 30.5". I'm a very good Senior Games time trial racer having won several medals at the local and state levels for the past several years. When I race, I'm riding on the nose of my saddle. I'm also soon to be 77 years old. All of the above is to set up my problem. As my knees (either one) approach the 12:00 position, they begin to significantly flare out so that my lower body becomes sort of parachute-like. NOT GOOD! This doesn't happen "much" when I'm on my road bike. I absolutely can not raise my seat post and saddle any higher on the time trial bike. So I'm thinking maybe 170 mm cranks might help solve the problem or should I just start racing using my road bike?
Tsapp