Isolate the male from the females.
Place a zip-lock over the end of a branch full of balls and secure it with a twist-tie.
When the balls open they'll shed their pollen right in the bag.
When all the balls have opened, carefully remove the bag, seal it, place it into another container (like tupperware of mason jar) with a bag of dessicant (that little bag that comes in medicine).
When correctly done, pollen can stay viable for at least 2 years.