Need I say more? Everyone knows when you press the 'F' key, you go into zoom mode with the reticule still visible. With a weapon equipped you're still able to fire it.
I was thinking maybe you can edit the camera as to where it's fixed and place it right above the hand. Of course some guns are bigger than others so it's probably only possible if you make it for the Tier Tactical set only or the L4D weapon set.
I'm not sure if it's possible at all or if it's been discussed but these are just my raw ideas. Let me know what you guys think since.. I don't know how to. :)