I know bugger all about bikes, however as someone who has ridden motorbikes, the first responder's answer about shoe covers sounds about right.
On motorbikes, the biggest enemy for your hands being cold, isnt the temperature,
its the 60mph wind hitting your hands. So you do something to block the wind and thats what does the trick.
Likewise it would seem logical that the solution to your problem is not trying to warm your toes more, but instead trying to block them from being hit with all that cold air while your cycling.
Edited: 28/02/2013 at 13:41