Glad you made it to the duck race!
Like Spud, I was going to mention both the birthday and cutscenes. You may be right that S2 doesn't have as many hidden scenes (I don't have a full list or anything, so I'm uncertain), but I think the trickier thing is that some of the events/scenes can be triggered only once, or that some prevent others from happening. An example: if you win the Wong chase QTE, you fight the thugs near Beverly Hills Wharf; if you lose, you instead fight them in an eatery. It's one or the other.
It probably helps to group the secrets/cutscenes by area.
I'm pretty sure Aberdeen/Wan Chai has the most unique events (e.g., the Chawan interactions-- try using the wrong sign at various places and you may get some rough results!)
In Kowloon, the main secrets involve the ability to play Afterburner and Hang-On in some very unexpected places. So too, depending on the method you use to find Yuan, you can end up at the Moon Child Orphanage for a somewhat depressing cutscene. (Most end up seeing it, but this scene can technically be skipped.)
In Guilin, the only secret I can think of involves the path you take to get to Bailu. Shenhua's dad wants some medicine, and if you choose one path, a cutscene related to that occurs.