I've looked into this as well some time ago, and the "commented config" files from BIS show gun 'mount points' for the commander's turret, but with the note that it is presently 'ignored'. I also recall seeing a post stating that the program memory point may or may not be active.
The cpp files only define the objects [PAUSE - I KNOW I AM OVER SIMPLIFYING HERE], but if the engine doesn't know what to do with the object, then it is just useless.
Where it stands now is that a vehicle has a turret object which has a main gun object which is also potentially linked to an offset secondary gun. Any exceptions to this would be doing 'tricky' stuff, like a commander action:
getpos (this, y+n, this)
left = getComTurDir - 45deg
right = getComTurDir + 45deg
lob smokegrenade left
lob smokegrenade right
Note, this is not real code of course, just something to get folks thinking...