Walt Some thoughts and ideas about fixed omni-angles.
So far I have made the odd angled prisms work, here's an example:

A very rough idea representation
And here were my steps:
1. Turn off ion emitters
2. Target structure on the other side of the armour holes with prisms
3. Lock prism rotation
4. Untarget the prisms so they don't damage friendly structure
5. Turn on Ions
And now I have working angled prisms, but it takes an unreasonable amount of time to do so it's not really viable in normal games.
Among many ideas here's one I that I think is easiest right now:
Allow prisms to "link" or point to friendly structure, with it being saved.
This would both solve it from the UI perspective and you don't need to add a bunch of functionality to save turret angles in designs (Although I would still love for that to be possible) and it makes such designs possible and reasonable to use.