I always just take the screenshots to the clipboard (hold down the control key), then paste directly into the image well in KM.
If the window is always the same size—or if the button is always at the same spot relative to the top left corner of the window, you could click at the offset from the top left corner.
If that's not true, you could move the window to a fixed size and location, then click at what will always be the same spot in the window, then move it back when done. A bit visually jarring, but it should definitely work (assuming you can move the Adobe window with KM):
-rob.