Originally Posted by bbattle
My LBS told me about some cogs that fit together so it's possible to have two on one side of the hub. If you hit some bad hills, you could manually change gears. Or carry a cog or two with you and swap them out.
Since you are accustomed to riding the bike you know what you're getting yourself into. You may want to map the route on one of these sites that'll give the elevations and grades. Maybe find some local hills that match the ones on the route and see how well you do.
No offense but that sounds like a solution that creates more problems than it solves. Changing cogs mid ride? Just roll a flip flop and you'll be fine. Or really take a geared bike.