When shots are overexposed like Keith's (I've done the same thing with IR820 and leaving the filter off, I seem to do it once every couple of rolls), you just need to use a longer exposure in the enlarger. The very dense negative lets the light through slowly, so it just takes longer for an image to form on the paper. Same principle in scanning - a film scanner has an exposure control which controls how long the scanner's CCD is exposed to the negative. Dense negatives just need more exposure.

As you can see, it's become very grainy and of poor contrast, particularly in the highlights, but you can tell what is there. If you did that much overexposure (even 4 stops = 16x, not even the 8 stops = 256x here) with digital or slide film, you would have a perfect white field from which absolutely nothing was recoverable.