i just finished a 2 week tour on my specialized allez with a 20 spoke rear wheel. i ran a 30 dollar rack from axiom, the streamliner road. it attaches at the brake bridge and the rear skewer.
it did fine, i actually didnt have any problems at all. i considered going with a trailer but i knew that i was going to go with a very minimal setup and i took a gamble hoping that the wheel would be fine.
i recommend this if you weigh less than 160 pounds and are taking less than 40 pounds of gear. if not i think it would be too much of a risk, if you loose a spoke on a race wheel you're stuck out there.