Easy! Just mount he SEI meter on a sturdy tripod, preferably with a geared head. That should make photography much easier.
With modern digital technology, it should be possible to devise a "tuneable" meter. In essence, the software would offer a histogram so you could adjust the output reading for each intensity of light and each wavelength. It might need a 3D histogram. Image stabilisation is a now very common technology so naturally it would be included to solve the half-degree problem.
Will anybody take up the challenge? I doubt it, but some mute inglorious App-writer might be reading this.
Half a degree is equivalent to a very long lens indeed. Here's a table of focal lengths vs angle of view. It stops at 800mm FL, – 2.6° on a 35mm camera.
I know some app writers. They are rarely mute