Disable Touchpad of Logitech TK820 on Xubuntu 14.04.2 LTS

How can I disable only the touchpad of the TK820 (Combination multi-gesture touchpad and keyboard)? I only could achieve disabling the complete input device. Any help or point in a direction is much appreciated. Its useless for me otherwise since I planned to put a normal mouse where the touchpad is. (Which works quite well for me)

edit 1:

$ xinput
⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ Microsoft Microsoft® 2.4GHz Transceiver v7.0  id=11   [slave  pointer  (2)]
⎜   ↳ SynPS/2 Synaptics TouchPad                id=14   [slave  pointer  (2)]
⎜   ↳ TPPS/2 IBM TrackPoint                     id=15   [slave  pointer  (2)]
⎜   ↳ Microsoft Microsoft® 2.4GHz Transceiver v7.0  id=12   [slave  pointer  (2)]
⎜   ↳ Logitech Unifying Device. Wireless PID:4102   id=17   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Video Bus                                 id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ Integrated Camera                         id=9    [slave  keyboard (3)]
    ↳ Microsoft Microsoft® 2.4GHz Transceiver v7.0  id=10   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=13   [slave  keyboard (3)]
    ↳ ThinkPad Extra Buttons                    id=16   [slave  keyboard (3)]

edit 2:

with evtest I saw, that the type of input read from evtest for the touchpad is always type 2. perhaps there is a way to ignore inputs of such type?

edit 3:

$ xinput list-props 17
Device 'Logitech Unifying Device. Wireless PID:4102':
    Device Enabled (140):   1
    Coordinate Transformation Matrix (142): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    Device Accel Profile (271): 0
    Device Accel Constant Deceleration (272):   1.000000
    Device Accel Adaptive Deceleration (273):   1.000000
    Device Accel Velocity Scaling (274):    10.000000
    Device Product ID (260):    1133, 50475
    Device Node (261):  "/dev/input/event16"
    Evdev Axis Inversion (275): 0, 0
    Evdev Axes Swap (277):  0
    Axis Labels (278):  "Rel X" (150), "Rel Y" (151), "Rel Horiz Wheel" (267), "Rel Dial" (268), "Rel Vert Wheel" (269)
    Button Labels (279):    "Button Left" (143), "Button Middle" (144), "Button Right" (145), "Button Wheel Up" (146), "Button Wheel Down" (147), "Button Horiz Wheel Left" (148), "Button Horiz Wheel Right" (149), "Button Side" (265), "Button Extra" (266), "Button Forward" (575), "Button Back" (576), "Button Task" (577), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263), "Button Unknown" (263)
    Evdev Middle Button Emulation (280):    0
    Evdev Middle Button Timeout (281):  50
    Evdev Third Button Emulation (282): 0
    Evdev Third Button Emulation Timeout (283): 1000
    Evdev Third Button Emulation Button (284):  3
    Evdev Third Button Emulation Threshold (285):   20
    Evdev Wheel Emulation (286):    0
    Evdev Wheel Emulation Axes (287):   0, 0, 4, 5
    Evdev Wheel Emulation Inertia (288):    10
    Evdev Wheel Emulation Timeout (289):    200
    Evdev Wheel Emulation Button (290): 4
    Evdev Drag Lock Buttons (291):  0

If you want to disable "TPPS/2 IBM TrackPoint", just run in terminal

 xinput disable 15

To make it permanent you can run this command as an "Automatically started application".

There are some other ways to automatically run this command at session start, but IMHO this is the easiest one.

As a workaround, I did the following to diasble the button/click of the touchpad. Not the cursor movements, only the click.

xinput set-button-map 9 "0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0"

Where 9 is the ID of the device, found with xinput list, and the number of buttons is found with xinput list 9. to enable the buttons again:

xinput set-button-map 9 "1 2 3 4 5 ... 22 23 23"