Oh, and I tried the aluminum foil trick with my clipless shoes this winter. Yup, it works. My feet stayed warm for a 90 minute ride around freezing temp with vented summer type Scott shoes and toe covers.

I'd tried the toe covers alone but it wasn't good enough below 40F, even with layered socks.

I wore layered socks, with the foil between the layers. Folded the foil up across the tops of the toes rather than under. Figured it would be less likely to cause pressure sores. But it's uncomfortably tight either way. After an hour the main problem was the pressure from the foil layer restricting circulation.

After one wearing the foil was tearing but it worked well enough to consider again.

Best solution would be Mylar foil lined toe covers, to reflect heat back without adding bulk inside the shoe. But I don't know if anyone makes such a thing. A Mylar foil lined snack bag might work in a pinch.