Wow, this is a popular thread.
Anyhow, I'm happy to say that the K-7 instructions from the video forum work for fixing the aperture and other settings on the K-5. I am also pleased to report that using a lens with an aperture ring makes things easier, as I had suspected. You can change the aperture on the fly during video recording and the ISO and/or shutter speed seem to compensate, unless you otherwise lock those settings with the AE-L button.
Setting it up is still a little bit of a hack, but works. Therefore, I would recommend a lens with an aperture ring. And I will eventually remove the ball bearing click-stop from one of my zooms to use it as a dedicated video lens.