Hot showers, they have the benefit of making you let down without stimulation. If your breasts get stimulated in any way, it'll only prolong your agony, but letting down without stimulation will ease your swelling without compounding the problem.
Another thing to think about doing is taking some Sudafed. It had the effect of almost drying my milk up when my son was only a few months old and I was normally producing enough to feed him all day and pump several bottles too. I had to fight to maintain my supply when I was on that medication. Maybe it would help.
Other than that and what you've already tried, I don't have any suggestions. This is just one of those things that we girls have to generally suffer through with a minimum of effective treatment options, like cramps.