Google time trial cranksets. I don't know what you will find but BITD there were some enormous chainring made. You could run a tandem drivetrain if you can install your derailleur and a BB to something in the middle of the trike. Run a single leftside 50 tooth off your pedal crankset and a 36 tooth leftside on the middle crankset. Run your regular (say) 50-35 on the right. A "timing chain" using 50 to 36 brings your gear rations to normal. I think that second BB needs to be an eccentric tandem BB so you can dial in the chain slack.

50/36 = 1.39 ~= 27/20 = 1.35

Now, that second crankset probably wants to be exactly where you are. And it is expensive and not light. (Not light? A plus going downhill!)

This stuff s fun to think about. I might get some more ideas lying in bed.

Ben - the guy who designed and built a triple chainline fix gear with three radically different gears for days in the mountains. Three 1/8" chainrings on a double crankset with a low Q-factor. Odd - yes, but it works really well. Yes, you do have to stop and pull out the wrench. It is a fix gear and there is no magic.