Some do have a drop feature, mine don't...They just have a zip down the side that goes from the top of the side (by the armpit) down to your knee. They zip both ways, so also used to ventilation.
I wear my bibs over all of my layers other than my shell, so easy access to the zipper up top...just reach under the shell, unzip to the knee, pull down your baselayer bottom and slide out the side. After some practice I now find it easier and quicker than normal pants.
And yes...I have used the same method when in the backcountry. Just keep your skis on to keep yourself on the top of the snow, and don't squat too low....brrr....