once you have broken out with the rash, scald it with hot water from your sink, bath, shower, whatever. This is the most painful, luxurious thing a person can experience as it releases the histamines that make you itch. I get about a twelve hour window of no-itch between scalds.
If you have been exposed but have not broken out, avoid hot water as it opens your pores and lets the oil in and eat prednisone or benadryl. Technu and a cold hose should rinse of any unwanted oils from a boat. I've heard dish soap dissolves the oil as well.
Once you get the oil in your system you can break out anywhere, so just because it's on the inside of your knee don't blame your thighbrace immediately.
If the rash gets really sloppy and messy, dab some bleach on a paper towel and paint the rash. It burns but it should scab up and go away, leaving your skin only slightly discolored.
If you're really brave eat a leaf or two. It will desensitize you, though I've heard horror stories about the intestinal reaction caused when it is processed. Can you say Taco Butt?