Ski pants would be cumbersome for riding any distance. A pair thicker tights under a windproof pair of pants, not the ski type, would be sufficient in -17*C. Below that, I might ad a pair of knee warmers under the pants.
The whole rigmarole is a hassle for sure and adds an extra 20-30 minutes, at least, to the time required to do the commute. But I take comfort in knowing that it's only for a few months.