This is a quick proof-of-concept example of using kterm's -e and -l options to launch a terminal program from KUAL with a custom interface using matchbox-keyboard's layout config, in this case a media player with basic controls (play/pause, forward, back, next, previous, volume +/-, off).

You need these, and anything needed to run them, including a supported Kindle:
KUAL: http://www.mobileread.com/forums/showthread.php?t=203326
kterm: http://www.fabiszewski.net/kindle-terminal/

Install the mplayer_test folder and contents in /mnt/us/extensions

To use this example you will also need mplayer, available at bottom of page here:
http://www.fabiszewski.net/kindle-xterm/

Install mplayer in any of the following:
/mnt/us/bin
/mnt/us/opt/bin
/mnt/us/extensions/mplayer_test/bin

or you can install it anywhere and edit /mnt/us/extensions/mplayer_test/bin/mplayer_test.sh to include the location in the path.

Read/examine mplayer_test.sh for more details on how this works.

Read matchbox-keyboard's README for more details on custom layouts:
https://github.com/Xlab/matchbox-keyboard/blob/matchbox-keyboard-xlab/README.md

Other possible uses for this technique:
- shortcut buttons for commands requiring alt/ctrl/shift combos
- controls for games (wasd and arrow keys are too tiny on default layout)