The Bernoulli equation should get you started with estimates but you will eventually need some real numbers. Do you have a way to measure static pressure or flow rate?
Could you simply pull a vacuum on the leaf container with the suction side of the blower? You would get more flow that way.
Generally all vacuum cleaners/blowers have 2 points to connect the pipe. One for vacuum and one for blowing.
Do you want this for academic purposes or for actually using on leaves?
Like montoyas said, Bernoulli's equation will help you, but you need some numbers.