The computer will fill in if you only put a few players on your Predraft player rankings.
Draft central>predraft player rankings>click view all>click edit my rankings>move from list of players to the right if you want 'em, left if you don't. If there's a player you want who's not listed, go to show and select ALL, then go, or filter if you know things like position. Finished? Click save, then click done.
Complicated but that's Yahoo. But then you'll be set. You can do this any time before the draft and need not be around for the actual draft.