I third the lecithin suggestion. Nothing else works for me. When I feel a painful hard lump forming, I take two capsules three times a day and feed as much as possible (dangle feeding sometimes sped the unclogging process). It seems to help emulsify any coagulated/stringy milk stuck in the ducts and allows the built up pressure to pop it out.
I found one capsule morning and night to be preventative, when I remembered.
I tried hot and cold, electric toothbrushes, massage, different feeding positions and cabbage, but lecithin saved me numerous times.