Place this in ~/.kodi/userdata/keymaps/customkeys.xml
<keymap>
<visualisation>
<keyboard>
<key id="166">volumeup</key>
<key id="167">volumedown</key>
<key id="168">skipnext</key>
<key id="169">skipprevious</key>
<key id="11">playpause</key>
</keyboard>
</visualisation>
<fullscreenvideo>
<keyboard>
<key id="166">volumeup</key>
<key id="167">volumedown</key>
</keyboard>
</fullscreenvideo>
</keymap>