I also have had recurring painful clogged ducts (and oversupply issues) here is what I found helps mine:
-the super hot showers (better than a heating pad)
- dangle feeding (or gravity as mentioned by pp) - you can also get the kiddo's chin lined up with the duct this way - which some people says helps
- and if I have one for more than 2 days I go see a Physical Therapist who does ultrasound therapy... worked 2 of the 3 times I went. I think you can find more info about US help from Jack Newman's book also info on kellymom.com
I also take lecithin supplements - Good luck!