As far as I know, -cg30,45,<n> (where <n> must be determined empirically) should mostly do what you want, but there are a few other options you might need additionally. Note that <n> is dependent on the FOV setting (e.g., -FOV=25). If you decrease the field of view, you must increase the distance to produce a similar result.
Adding -ZoomMax=10000 to the command line will decrease the probability of the camera being pushed away due to being too close. (LDView by default doesn't allow the camera to get close enough to the model so that rotations could result in it being inside the model.) You might instead be able to use -ViewMode=1 (which switches to fly-through mode, where the zoom level isn't constrained at all). However, I don't think I've ever tried that on the command line. The viewing mode is generally useless for command line snapshots, since there's no interaction, but since zoom contraints are disabled in fly-through mode, I think -ViewMode=1 will accomplish that on the command line.
By default the model is centered, so the its origin is ignored. Use -ModelCenter=0,0,0 if you want to disable the auto-centering.
Adding -ZoomMax=10000 to the command line will decrease the probability of the camera being pushed away due to being too close. (LDView by default doesn't allow the camera to get close enough to the model so that rotations could result in it being inside the model.) You might instead be able to use -ViewMode=1 (which switches to fly-through mode, where the zoom level isn't constrained at all). However, I don't think I've ever tried that on the command line. The viewing mode is generally useless for command line snapshots, since there's no interaction, but since zoom contraints are disabled in fly-through mode, I think -ViewMode=1 will accomplish that on the command line.
By default the model is centered, so the its origin is ignored. Use -ModelCenter=0,0,0 if you want to disable the auto-centering.