How about making it a Dinglespeed? Run your offroad ring on the inside of the spider and your street ring on the outside. Same with the cogs in the rear. If you have a threaded rear hub, WI makes a dual cog called the dingle (?) with combos of 17/19 & 15/17 I believe. If your ring/cog combos add up to the same amount of teeth, you can run the same length chain and switch ratios just by dropping your rear wheel and switching the chain over.
Ex: 32/19 = 34/17 OR 34/17 = 36/15
Then you won't need a new rear wheel, shifter, derailleur, hanger, and have to eff around with the whole shebang.
If your rear hub takes splined cogs, grab a pair of surly cogs and mount them with the shoulders facing each other and use spacers accordingly to get your chainline straight.