Think you can achieve this by using POI's & set the heights of them & have the default gimbal pitch mode in the mission hub set to "Focus POI".
For instance, if you have your first WP at 30m height, then place POI #1 right in front of it (or on top of the WP) & set the POI height to 1m & set the WP so the camera will focus on POI #1 ... this will see to that the camera is pointing down. For the second WP (also 30m height) you do the same, place POI #2 right in front of it but set the POI height to the same height as the WP (30m).
If I do a simple mission like this it will start out with the camera down & on the way to WP2 it will gradually pitch up the camera & reach a horizontal camera pitch when it reaches WP2... added a third WP also to pitch down the camera again, it works... at least when I test run the mission via Virtual Litchi Mission (VLM) in Google Earth.
View attachment 142666
And here how it looks in Google Earth ...