Hmm, maybe one of these (crank based three speed gearbox) would not impede the fold.
Gearbox | Efneo
from the Helix Kickstarter comments...
[h=3]Creator
Helix Labs Inc. on September 29[/h] @
avi Karminer, the Efneo is a gear box that we will be looking in to further. Of all the crank gearboxes we have seen it is the most likely to be compatible.