Allow me to clear up some facts; You CAN make a Pentax K to Pentax K Focal Length Reducer.
The Issue is that Kodak owns the patents. And the designs are sorta volatile; When properly matched to a lens, they increase resolution and improve image quality, but... You need multiple designs, because the wide converter is sensitive to the lens's exit pupil location, the rear element location, and the rear element size. You'd end up with a few very nice matched versions though.
Possible, yes. Rewarding, yes.
Easy to do right now? Not at all. I'm sure with enough time and effort one could build some, but Kodak has a very very strong patent on the designs, and I'm pretty sure their lawyers would suck to deal with if you decided to sell some...
Here's the Patent and a Lens Diagram. Enjoy!
http://www.google.com/patents/US5499069