This works for me, I can't deal with not having cleats at work either.

Shoes: Lake DH*, 2 sizes too large
1st layer socks: Med[rated to -10 or -20] to Hvy[rated to -40] weight wool, Smartwool brand if you can afford it (I can't! $^%*ing $40 socks)
2nd layer socks: Neoprene diving or kayak sock booties. $11 or 12 bucks and a great investment

The sock setup really works, if you're working in -10 or less but need to stay warm enough to avoid frostbite from windchill then you probably can't do a breathable/dry foot option that'll work when the windchill while riding is doubled or tripled. The wool against the skin insulates when wet, the neoprene insulates the wool from wind and keeps the heat in. You definately want to take your shoes and socks off after working all day though. It's a wet but warm arrangement. If you've got good wool socks you won't feel wet while wearing it though, and never squishy wet.

*I got these on ebay cheep. I know some guys here in canuckland that use this arrangement with any cleated shoe they can get cheap and 2-2 1/2 sizes too large. For regular cycling shoes the trick is to duct tape the vents in any shoe, winter ain't the time for em.

That got me through last winter, which wasn't too bad a winter really though we did have some cold days and I had to work em.