Since it seems that the ultimate solution to healing is to reduce the pressure of the internal sphincter, I wondered if anybody has had any luck with meditation, yoga, or any other relaxation techniques?

Maybe I'm just getting desperate, but the idea at least seems somewhat plausible to me. Anyone ever tried and noticed any improvement?

Yes, it has helped me a lot. In the beginning when I was in pain it was hard to relax at all. But even then usually after 3PM all pain went away and I used the evening to do progressive relaxation since I was calm. Before you begin any relaxation attempts, focus on your forehead. Is it tense? I find that all day long my forehead is tense and I have to consciously relax the muscles, from there my entire body relaxes. Now, throughout the day, I have developed the habit to become aware of my forehead and relax it as many times as I can. In the evenings I like to watch cooking shows which relax me tremendously and I censoriously dip into a very relaxed state and think positive. I imaging as my body has never had anything wrong and everything is working properly. When relaxed, try consciously to focus on your pelvic floor and let go of all tension. Put your legs up against the wall and put a pillow under your back, so that your pelvis is slightly above your heart. That will cause blood flow to the area. However, in your condition, please consult with your doctor first before elevating your legs above your heart.
At the end, it's all in our minds. I believe that pour thoughts and emotions send signals to all our cells and they respond accordingly. Start sending signals of healing and well being and soon they will start responding to these commands.

Thanks for the response! I'm going to try some guided mediatation/relaxation and see how it goes. At the very least, it will be good for me mentally!

The internal sphincter is made up of involuntary muscles so relaxation can only do so much in terms of reducing spasm. More localized methods like ointments and surgery are what help it relax better. Of course, stress makes all muscles tense up in the body and can cause fissures too, so meditation can be beneficial for healing.