Today, I hacked together a PXA27x matrix keypad driver for U-Boot bootloader. It behaves as a usual stdin. Then I made ZipitZ2 utilize this new driver. I also implemented support for various modifier keys directly into the driver for convenience's sake. The driver still has a few rough edges and needs some more care, but it does it's job on ZipitZ2 well.
The source code can be found in u-boot-pxa -devel branch.