My experience with trying this just to see how they would work was that not only did the pads have to be adjusted really close, but it made the brakes "grabby" or too easy to lock up. The added weight on the tandem might take care of this, but you'll probably find that you need to use the full travel of the brake lever to get them to work and if you have a steep descent you just might wear off enough pad that you can't get the lever to work at all. One of those liabilities that TandemGeek pointed out shops need to be concerned about.