You can also mount a grip shift:
On a Hubbub bar end adaptor (down this page)
http://www.sheldonbrown.com/harris/shimano-nexus.html
On a Minoura space grip, stood off from the bars:
Or cheapest of all, on an MTB bar end, mounted to your stem so it protrudes sideways further down than the bars. This is one I want to try.