When snowfoaming, or spraying with APC, use a brush one the black plastic/rubber bits. I use megs triple duty brush. If you want, it can be done separate to the rest of the car. Use APC on a brush and then work the trim with the brush. Wipe or rinse and once dry, use your trim detailer.
The plastic won't mark but am not sure about the rubber - tend to use a softer brush on these.