Alright I was in IF testing a new talent spec when I saw a lock log on and soul drain a target dummy. She did this a few times and then ported away. I whispered her asking if she got soul shards from the dummy and she replied yes. I was intrigued by this and decided to check on my 52 lock on a 60 target dummy. It actually works. Since they changed the spell from killing it to just damaging it it will work like this. I included two pics with the same text at the top to see that I didn't cut and paste anything.
I searched the forums for
Soul Shard
Target Dummy
Free Soul Shards
and all results came back with nothing of this trick. I guess it isn't really an exploit. But it would be useful to raiding locks so they can have a full bag of shard before the raid instead of trying to get them off the trash and fights.