I found something interesting in method mousePressed(MouseEvent a) in class ContentPanel (in ReaderSDK-impl.jar). A variable is increased or decreased by 40 (depends on value of a.getButton() is 8 or 7).
As I watched "showlog -f", I see Button=7 when I tried to pinch with 2 fingers, and Button=8 when I tried to stretch with 2 fingers.
So, if my guesses are correct, I can change the zoom factor by replacing 40 with some user-defined values
. Next step is learning how to do it with jbpatch