Shift ahead of time in back. Then all you have to do is hit the left shifter with your knee. Or, like I did when I broke my seatpost - coast and lean the bike against your thigh, reach down and shift, return to the bars and peddle. Steep enough hill, not happening! (I muscled a hill on the 42-14.)
DT shifters - plan ahead. A quick sit and shift while you still have speed. No? Pay the price. This was set in stone a million years ago. (Not really. Back then it was stop and flip the wheel or just pay the price.)