First I have used Light room a bit, and I should probably go ahead and get it, but that is another posting. From what I understand, you can create your own lens profiles for Lightroom....
I am wondering out loud (since I have not tried it), if you could mount your camera on a tripod, and take two images of a "brick wall" (or similar "target"). One image with in-camera lens correction and the other one without in-camera lens correction. Then via the Lightroom lens profile creator, use the non in camera corrected image to correct it (in some way), to match the camera corrected image. If you can do this, then you essentially have a Lightroom lens profile that replicates the Pentax in camera correction.
Just a thought....