As Adam mentioned, while you can access the DEBUG menu option within the K-x to make AF adjustments, any changes will apply across every lens you mount, not just on a per-lens basis.
If this is still useful to you, there is a tutorial for doing the K-x DEBUG menu adjustment
here. There are also lots of threads in this forum about the issue that you may like to explore.
Although I haven't tested it on my K-x, perhaps the easiest way to call up the DEBUG menu may be via the options in the
PKTether program, once you have connected your camera to a computer via a USB cable.
EDIT: altopiet beat me to the RH link.