You can, but you may get some "extra" seeds, all it takes is for a little pollen to get loose and you'll have a few stray seeds, but nothing heavily seeded except the buds you apply the pollen directly on. Back in the day (Humboldt in the 70's), I used to always grow one good quality male plants that I purposely kept small, as soon as a few pollen sacks opened I would stand in the doorway to the greenhouse tap the male plants twice, let the wind blow in and then close the door and destroy the male, alway got enough seeds for next time. I tried to do it very early when most of the ripe/receptive calyxes were in the nodes, so not a lot of seeds in the actual buds.