There's not a lot you can do, but thankfully the plants that are coming up in late March are pretty hardy.
You can certainly mulch them up a bit by piling any extra mulch you have on top of them. That will help protect the leaf quality and they'll look nicer once it gets warmer.
Even if you don't they'll probably still bloom and the leaves will regenerate.
Of course, much like covering plants in the fall, you can rig up a sheet and cover them. It might help a bit, but the season is working against you now. Whereas in the fall, the earth is warm and covering helps capture some of that warmth which helps the plants, in the spring, we have no such help from a frozen soil.