There are a few standing poses that we can apply the yin techniques to, but remember the general principle that "yin tissues need a yin form of exercise and yang tissues a yang form of exercise." It can be dangerous to mix these up. [You may want to read this section for a bit more on this topic:
http://www.yinyoga.com/ys1_0.3_theory_of_exercise.php]
The Dangling pose, for one example, is a standing pose where we want to relax the upper body so that we can obtain a nice traction for the spine. However, because the knees are bent, we don't want to hold this pose very long: 2~3 minutes at a time is enough. This pose is yin for the upper body and yang for the lower body. We could do the same, as you suggest, for Prasarita Padottasana A (wide leg, standing forward fold), but again, this may be too muscular to stay in it for too long. If the legs can relax, then feel free to stay longer.
Triangle, warriors, and many other standing poses do not lend themselves to a yin approach because we have to engage so many muscles to hold ourselves in the pose. In general, any pose where you can relax for a long time, softening the muscles, can work as a yin pose. The key question to ask yourself is, "what is my intention?" Why do you want to do that pose? If you are trying to work a specific area or group of tissues, know that. There may be other, safer ways, to work that area and obtain your goal.
Cheers
Bernie