Bend them the other way. Start with all fingers open for zero, and curl them as needed. You only need to move them a bit, so even twenty (thumb and ring finger back, the others curled) isn't too hard.
you can cheat it quite easily, just hover your hand over a table or surface, and touch your fingers to the surface to indicate a 1, and dont to indicate a zero, works on your leg, or someone elses, if you felt like it i guess.
great point.. and if after the 12 you start touching your thumb to the other side of those phalanges, you now have 24. now each time you go through the 24 cycle, your other hand can tick along the same cycle like an hour hand. now you are counting to 550+ with 2 hands.
I was able to get to this number: 1 048 576 by using base 4 and making each finger a different "10" s place using each finger segment and the tip of the palm below it but you have to keep track of how many of each order of magnitude you have by yourself. Alternatively, just use a piece of paper.