I have just posted 3 ideas for a USB Mouse module to the photo
section on the newsgroup site.

http://launch.ph.groups.yahoo.com/group/Doepfer_a100/photos/browse/8b4d

All versions have CV outs for left/right, Forward/back and wheel Up/
down. I see this as a bipolar voltage that acts like the mouse - it
is additive in that if you lift the mouse up and then continues it
will just add and subtract from the last setting till it reaches it's
full range and just stays there. The knob scales the sensitivity of
the mouse Not it's range which would be -5v to +5V. They all also
have a Position Reset button that returns the CV outs to Zero position.

The fist one is the most basic and was designed using the same
metalwork as the A-198 Ribbon controller module to save cost. Because
of that it only has one button gate outs. A led shows when the button
is pushed and another lights when the mouse is moved.

The second version is the 2-button version and has gate outs for both
left and right buttons.

The third version is the full feature set version. It has 2 button
out gates but also gate outs that go high when the mouse is moved in
that axis or when the wheel is moved. Because of space restraints the
Position Reset button has been removed but it's function can be
replaced with the wheel button on the mouse.

Of course a mouse does not have to be used. Any USB controller that
delivers mouse-like data can be used as long as they don't need
special drivers. Things like touch pads, trackballs, flight stick,
and steering wheel game controllers all have versions that you can
buy that output standard mouse control data.
-James