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One of the comments mentions a do it yourself double chainring he uses without a shifter. A response suggests that you nudge with your foot to the smaller ring (dangerous?) and getting off the bike and using your hands to go back to the larger ring. That seems to ruin any ride IMO.
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I tried that on my Joey Airnimal soon after I built it up. I wanted a wider range of gears, bought a double crank and installed that. I very soon got tired of stopping to get my hand dirty from upshifting the front. And my shoes got greasy rather quickly from downshifting.
Later I added a Sram Dual Drive to my Joey. That gave me the wider gearing that I wanted.
If you want to try two chainrings, I suggest a wax type chain lube. Over a decade ago I used an oil based chain lube and that is what I used during my two chainring experiment. Now I use a wax type chain lube, the chain is a lot less greasy.
The newer Airnimal Joey frames can be fitted with a front derailleur, unfortunately my older frame can't.