Start by not killing off your males as soon as you detect them. Instead, isolate them and collect the pollen. Freeze it. When you need seeds (a shitload, really. A SHITLOAD.) De-freeze pollen, place in bag, pick out a fertile, yummy girl, wrap bag around a buddy branch, shake vigorously. Viola, pollenated. Blueberry is pretty good to do this with. (Btw: Don't let that pollenated female get near the others if you still want your bud crop to be sinsemilla.)