Thank you everyone for your ideas/suggestions. Today it was 'only' -20C/-4F, so I tried Ziema's idea about adding an additional layer on top of jeans. I wore lightweight training pants. It's amazing how much warmth a single, lightweight additional layer can give. I was out for 2 rides, each slightly longer than 1hr, and I was almost comfortable. The only problem was my gloves, which let the wind through. I think I'll buy some lobster gloves tomorrow