Is it possible to toggle the trackball as a scroll wheel using Karabiner?
Try putting this into your private.xml file.  Select the top option (Toggle CursorMove -> ScrollWheel) in Preferences/Key Change tab and this will toggle the option below (using simultaneous press of trackball LEFT/RIGHT buttons).  You could use KeyToKey instead of SimultaneousKeyPresses if you just want to use a single trackball button press.

&lt;vkopenurldef&gt;
    &lt;name&gt;KeyCode::VK_OPEN_URL_SHELL_toggle_cursormove_scrollwheel&lt;/name&gt;
    &lt;url type="shell"&gt;
        &lt;![CDATA[    /Applications/Karabiner.app/Contents/Library/bin/karabiner toggle private.pointing_relative_none_to_scroll    ]]&gt;
    &lt;/url&gt;
&lt;/vkopenurldef&gt;

&lt;item&gt;
    &lt;name&gt;Toggle CursorMove -&gt; ScrollWheel&lt;/name&gt;
    &lt;identifier&gt;private.toggle_cursormove_scrollwheel&lt;/identifier&gt;
    &lt;autogen&gt;
        __SimultaneousKeyPresses__
        PointingButton::RIGHT, PointingButton::LEFT,
        KeyCode::VK_OPEN_URL_SHELL_toggle_cursormove_scrollwheel,
    &lt;/autogen&gt;
&lt;/item&gt;

&lt;item&gt;
    &lt;name&gt;CursorMove -&gt; ScrollWheel&lt;/name&gt;
    &lt;identifier&gt;private.pointing_relative_none_to_scroll&lt;/identifier&gt;
    &lt;autogen&gt;__PointingRelativeToScroll__ PointingButton::NONE&lt;/autogen&gt;
&lt;/item&gt;