This mod is based on some sketches I made, which I said I would upload for others to try. Rather than give untested advice, I have successfully made the modifications and will present them here for all my fellow garage hackers and bike builders. This modification would probbaly work for any recumbent with a 1.5 inch or larger main boom and linked steering as well.
Although you will have to make a few cuts to your frame, the good news is that you will not need to source any extra parts except for the handlebars, and the surgery can be done in an afternoon. Under seat steering allows the arms to rest in a more relaxed position beside your body, and allows the pilot to climb in and out of the bike without having the steering stem in the way. Under seat steering does however feel quite different than the conventional handle bars out front system, so think about this modification and read it through before you start up your grinder.
The full free plan is available now at www.atomiczombie.com .