Hi, welcome to the CBPS forums, hope you enjoy:
I looked at the moonlight source:
https://github.com/xyzz/vita-moonlight/blob/vita/src/input/vita.c#L399So this would be the area that mouse states are handled and I am guessing that two fingers is scroll, a quick tap is click, and as you said moving is handled relatively.
The function that controls mouse movement can be seen here:
https://github.com/xyzz/vita-moonlight/blob/vita/src/input/vita.c#L105It looks like the delta is calculated between the new and old points to modify the mouse position creating the relative movement you see.
In theory, I'm guessing this could be modified to be an absolute mouse-input area as you are requesting with some sort of scaling to account for any aspect ratio or resolution changes.
However, I don't have a PC capable of testing moonlight stuff.
Hope this helps though kek.