I did the same thing Rydernow did; rotated the stock shifter arm rearward.

Remove the socket-head screw holding the arm to the trike. You must back the screw all the way out because it fits in a grove in the serated shaft from the gearbox. Gently prise the shifter arm off the machine. This may require some prying with a flat bladed tool, or even resorting to a two-armed gear puller. Once the arm is off, put a little grease on the serations and press the shifter arm back onto the shaft at the desired new position. This may require a little judicious pounding, but it should go on fairly easily. Reinsert and tighten the socket-head screw.

I can now shift mine just using my foot without any problem, almost as easily as on a bike.
BS