First of all, let me wish you All The Best for your final (partner) round. I believe, I can give you valuable insights, since I have recently accepted an offer for the TA practice (Generalist role) in one of BCG's Asia offices.
I'll try to keep this short and answer your questions:
1. Tips / tricks on how to prepare for the final round: Try to visualize all the case interviews that you have passed so far and then pin-point the one's where you struggled the most. Was it communication or structure or math? Focus more on that weakness. Most probably, in the final round they will test that area of weakness once more.
Be prepared to be handed a lot of data on paper (tables / charts) during the case. Focus on identifying the pieces of data that will help you solve the case and ignore data that may not be useful enough.
Tip: Study the profile of the partner who will interview you. Which 2-3 industries does the partner focus on? Read about the Digital trends in that industry.
Tip: You will most probably be given a case from one of those 2-3 industries.
2. There are hardly any good IT / Digital related cases available online. And remember that it is not necessary that you will be given an IT / Digital focused case.
Tip: However, the trick is that although the case may seem like a normal strategy case, the final recommendation may lead to a digital related solution (like automating a task or creating an online presence).
I'll finish off by saying that I came across this question by coincidence :) Will request you to reply and let me know if you get an offer and which office will you be joining then. We can exchange contact details and then share tips on preparing for the real journey at BCG :)