spankey is right, you do not have to use one big screen, but using smaller individual screens for each plant that will make one big screen when put together you can design your pots with the screen attached just for one plant so if you did train and find out it was a male you could pull the whole pot screen unit with the male from the flowering room.
the down side to that is that you may be training males and any training you did was just a waste of time, and it takes up more space and may not use up all the space available in the flowering room.
but a scrog can be done from seed its just going to be done a little different.