With a limited aimrange is it really that big of a deal? Just get the velocity of the shells such that they'll eject out of that.
Or, of course, you could use a little lua script on the actor to spawn an emitter that spits out shells when the actor is firing.
http://pastebin.com/m54c79f43Here's a rough lua script, untested. It'll create a shot emitter particle at a rough offset, you'll want to fix the offset and make sure to use the right presetname + .rte name. Oh, and make sure to attach that script to the actor. And that your gun isn't emitting any shell casings itself.