If chain is not super tight, it usually works fine to push the chain off front chainring, manually move chain to the other rear cog and then partially engage chain back on the other front chainring and pedal it back on, no need to even loosen and re-tighten the skewer. Works only if the sum of all the front and rear teeth on both chain-paths are same.

10+ years after the original post, I still have three different bikes setup as budget dinglespeeds. Probably my favorite is a fatbike conversion I setup with the 2-speed drivetrain, works well to use the low gear for days of slow trailblazing through soft unpacked snow conditions, the other higher gear for days of riding on faster packed trails.