A travel-agent type setup should be able to give me enough pull if that's an issue. Finding the stops seems to be more of an issue. If I ever get around to building the wheel, I'll have to give it a shot.
It seems like there's renewed interest in planetary hubs, I don't know why Shimano hasn't produced a drop-bar compatible shifter. Hell, even a crappy old thumb shifter like an old Sturmey Archer (or old Shimano) would work acceptably well. Better than the twister on the bar plug trick.