Several months ago someone posted about the Sherman method in menstrual_cups . That post got deleted, but the gist of it was that someone in Israel is teaching a method where women can control their periods. It seemed like the idea was that you can sort of "blow your os" the way you blow your nose. But you had to go to the seminars in Israel to learn how to do it. I can't find the Sherman Method website now. Maybe it's gone, or maybe it's not showing up in my search because the site isn't in English.
Anyway, shortly after I read that post, I started doing some breathing exercises called SRI. I noticed that when I focused my breath on my lower abdoemen while I was on my period it caused me to gush. When I do that at the beginning of my period it starts heavier and I have only one heavy day and then spotting. Without doing the exercises, I have a heavy day, a medium day, then spotting. I haven't been able to control my periods as much as Sherman claims that you can under her instruction, but I'm getting better with practice and it is an improvement!
What I do is I place my hands on my lower abdomen. As I breathe in through my nose, I imagine that I'm filling the area under my hands with energy and breath, expanding the tissues. Then I breathe out through my mouth and focus on contracting and emptying the area. There is no bearing down. The pelvic muscles are relaxed. I do a few breaths while I'm in the shower or on the toilet. When I do this at the beginning of my period I have some really heavy bleeding for the next few hours but it gets my period over with more quickly and is less crampy.
Maybe it's all in my head, who knows, but it could be worth a try if anybody wants to give it a shot. Let me know if it works for you!