clams in the freezer by accident?

The safest, and though it sounds counterintuitive, also quickest way to thaw anything is under cold running water, even if it's the barest trickle.

I'm guessing that many won't but feel free to try...put some butter, a splash of wine in a skillet and try...either way you can add the other ingredients later.

I've had frozen mussels in sauce that just needed steaming and they open fine.

Yes, they're fine but now instead of letting them open in the shell you'll want to shuck them. Freezing actually makes them easier to shuck. You want to save all of the juices in side so if you're trying to hasten the thawing don't rinse them with water...put them in a stainless steel bowl and then put that bowl in another with warm water. Shuck and save all of the juices and cook in your pasta sauce.