If ya hold your mouth right, and have been living a good clean life, like Momma told ya to.......the plastic end caps will swell with the expansion and MAYBE let the rad live.
And MAYBE the soft plugs, which up north we always called them FREEZE plug will push out and save the bock.
As far as the best way to thaw it out...I am not sure.
I wonder.....if since the rad is only half full....would it help to ADD some anti freeze so if anything does thaw.....it won't re-freeze. I know it would not penetrate the block but it may be worth a shot.
I think I would be tempted to take off the water hoses, and remove the thermostat. It MIGHT even be worth it to pull the whole water pump....ANYTIHNG to give the ice room to expand.
Let us know how this turns out. Good luck!