Question : I am curious to know the ayurvedic understanding of, and approach to curing stubborn anal fissures and hemorrhoids. I know that these afflictions are related to the modern, sedentary lifestyle and nutrition.
Answer : In the ayurvedic text Sushruta Samhita, the treatment for fissures and hemorrhoids is discussed in great detail.

You can manage this problem with the proper diet and lifestyle, but it's good to see a physician.

As you mentioned, sitting for long periods is and etiological factor. You need to pacify Apana Vata and if there is bleeding, Ranjaka Pitta. Here are some tips that will help:

Dietary and Lifestyle tips:

Take Liver Care syrup, 1 tsp. in the morning and at night.
Take psyllium seed husk, 2 tablespoon in water before bed.
Eat nutritious foods with water-soluble, easy-to-digest fiber such as whole, juicy fruits, white pumpkin, carrots and cucumber.
Avoid hard fibers, such as hard, mature spinach, which can scratch the rectal area.
Add yellow mung dahl to the diet. (Available at Indian grocery stores.)
Avoid spicy-hot and citrus foods.
Cook with coriander, and a little cumin and turmeric.
Don't skip meals.
A morning walk is a must.
Avoid continuous sitting. Take breaks and stretch.
Go to bed early, by 10 p.m. if possible.
Don't hold bowel movements or urine.