Ismael's side trail 1-0 to the Swans after the first leg at Oakwell and can only progress to the showpiece at Wembley on Saturday week if they win at the Liberty Stadium by a margin of more than one goal over ninety minutes or possibly extra-time - or prevail in a penalty shoot-out.
Swansea have already won all three matches against Barnsley this term and have yet to concede a goal.
Famously, Barnsley triumphed on spot-kicks when these sides met in the League One play-off final at Cardiff's Millennium Stadium almost 16 years ago - after the game finished 2-2 after extra time.
While penalties is one possible scenario tomorrow, Ismael has been focusing all his energies on his side wiping out their first leg deficit on securing the margin of victory that they require in normal time or extra time to seal their passage to a fourth play-off final in the club's history.
On whether his players have been practicing spot-kicks, Ismael said: "No. Because if you think about penalties, you think about something that 'could' happen.
"I have ninety minutes plus to decide the game. This is my mentality. I do not want to practice the penalties because I prepared the game from the first minute to give everything to have a decision after the ninety-plus minute.
"If, near, almost...Just be focused. It is a tough game and everyone knows exactly what this means. If you win the game, you are in Wembley and it is the reward for all the four teams who are in the play-offs.
"All the four teams want to go to Wembley and this is the only (thing) in my mind at the minute - to prepare the guys to have the performance and make it happen.
"You have to control your emotions. We have one game to play."