Mountain Tamer could get below 20 for the granny, I think that only works with a 74mm BCD triple crank however. It would be a complicated installation, new crankset, maybe new bottom bracket. But with the existing rear wheel and 34t big cog, a 17t granny on the Mountain Tamer could result in about 13.8 gear inches (approximate).
Mountain Tamer Triple adapter - LOWER GEARS for bikes of all kinds

If you try this, carry a few spare quick links in case you start snapping chains, that would be a LOT of tension on the chain. If it was me, I would be nervous about getting my shoe cleats out of the pedals fast enough if I snapped a chain on a steep uphill at less than 3 mph speed. Snap a chain and you might be going backwards in less than a second.

I hate steep hills.