If the problem is that team B wants to know what team A will be fielding, I guess the proper way is to declare the ball ready for play, and if team A will come out, hold the ball until team B comes out, and then enforcing a DOG against team B if the play clock expires. In any event I would not let team A run a play unopposed, that's calling for injuries if team B "players" come on the field during the down.