Pienaar, who represented Ulster in the 2012/2013 season finale in which they went down against Leinster, believes that the team has a chance despite being written off against the unbeaten Dublin outfit.
The star player, who earned 88 Test caps between 2006 and 2015, believes that Ulster will need to be at their best, but he said the bounce of the ball could aid them in a final where the pressure will be intense.
“Ulster last won the competition in 2006, and we were in the final in 2013 when we lost against Leinster,” said Pienaar. “For a small place like Belfast it is a massive achievement.
“The club has a great tradition and they are regularly in the semi-finals, so they know what they have to do.
“Facing a team like Leinster isn’t easy because they have won so much and they have been in these situations so many times, so they know how to react.
“But a final is anyone’s game. It takes one wrong bounce and it can go any way.
“I’m excited to watch the game and really hope Ulster can give Leinster a real go this weekend.”
Pienaar lauded his former team’s fighting spirit in the semi-final win over Edinburgh and said: “Having watched the semi-final, I think they were in a bit of trouble at halftime, but they showed a lot of character and fight to come back and win the game at the end.
“I’m still a massive supporter of Ulster and I’ll always want them to do well.
“I’m overjoyed to see them in the final, but it will be difficult to beat Leinster, who will definitely arrive as favourites.
“But as we have seen in the past, anything can happen in a final, although Ulster will need to be at their best.”
Pienaar also praised Ulster coach Dan McFarland for steering the side to the final in only his second year at the helm.
“Dan will prepare them well for the week and they will have a definitive plan to try and take them on,” said Pienaar. “Last year in the Champions Cup quarter-finals, they really took Leinster on and eventually just lost by two or three points if my memory serves me correctly.
“Ulster play them on a regular basis and they know Leinster’s strengths and weaknesses well, so if there is a team that can give them a go, it is Ulster.”
Asked what words of encouragement he would have given his former team-mates, he said: “Don’t let the occasion get the better of you.
“Obviously there won’t be a crowd, so you will need to generate your own energy for the game.
“They are good enough and they know Leinster well enough to know where to strike.