Yeah, I would not do it. First, in my experience it's never once been necessary, and I've done this more times than I can count over the last 30-odd years. Second, as Raymont points out, it's more likely to make things harder for your plant than easier - by the time it's reached a point where you're doing this, it already has a well-developed root system. If you add rooting powder to the soil above the root system, the rooting hormone will be carried down through the growing medium to the root system, which can shock the young plant or seriously damage the existing roots. Rooting compounds are some extremely potent shit.
This is another one of those cases where the less you do for your plant, the more you're doing for it. As Raymont says, it's critical to keep the soil around the buried stem moist, but not soaked. Just water your plant normally, and in a couple of weeks you'll have good roots coming out of the old stem.