You need to remember that your speed is relative to the earth, not the inside of the elevator. Momentum is based on speed. When you are falling you pick up a bit over 20mph per second that you are falling (at least for 6-7 seconds when air resistance starts to be an issue). So if you have fallen for 5 seconds you have gone about 400 feet (30+ stories) and are moving a bit over 100 mph.

How much speed you think you can get into a jump? Even if you could get youself up to 10 mph (which is unlikely), you still hit going 90 mph at the bottom.