Are they large enough to tie up? Use twine and loosely wrap. If you can, go out and occasionally brush off the snow - it's the weight of the snow that snaps branches. If you have Emerald Green Arborvitae, the weight may bend over complete branches to the ground. Try to brush off snow ASAP and tie up the branch and it will usualy recover. Next year build wood cages over them or put burlap over them.

Any suggestions on a last minute way to protect American and English boxwoods from snow? last winter I just brushed the snow off with a broom but with 2 feet there won't be anywhere to brush it as some may be covered.