It's doable, but if you are targeting higher carbs only at pre and post-workout meals, then sure, it's harder than allowing for the higher carb side items at all meals. You'll probably have to force yourself to eat more in this case. When I am doing higher carb days, I tend to have a protein + carb meal in the morning, eat fewer carbs and lunch (protein + fat + veggies), then have a PWO drink and my evening meal, which is protein + carbs as well. I never have a problem getting to 300g on workout days. As a snack, consider adding in homemade popcorn, at about 20g net carbs per 3 TBSP. You can eat it within the PWO window too.