I wouldn't worry about it. Olive oil does have a lot of calories, about 120 calories per tablespoon. At 8 tablespoons per 1/2 cup, that's about 960 calories. You're only going to flush every 2-3 weeks and pretty much skip dinner when following Clark's procedure. Plus, olive oil is good fat and has a lot of other benefits.
I would be much more worried about weight gain if the flush required eating 4 bagels instead.