First of all, I am sorry if this is a repost, but I just figured this out by myself. I couldn't find anything regarding this using the search function.
I was just thinking today, is there a way to boost your way to a desired item for your low level character with your high level character? The answer is no, right? Because you can't be online for both killing the boss and taking the loot with your alt.
Wrong.
Here is a technique I tried, and it worked like a charm.
1. Open two versions of WoW on your computer, and log in on your "soon to be boosted" toon.
2. Get your toon in a party, using a guildie or friend.
3. Log in on your other character, thus forcing your first character to disconnect, and get invited to the same group.
4. Set looting to master looter, and make yourself party leader.
Now the fun begins. Get both your characters inside an instance of your choice and start clearing it with your high level.
When you get to a boss, log first on your low level alt, then as quickly as you can log in on the second wow client again and onto your main. As you can see, now you are online on both characters!
Kill the boss fast as shit, and master loot the loot to your toon.
I can just add that this probably works just as well with commands that disconnect you, and then you only have to run one client. Couldn't figure out any disconnect commands on the fly, so I tried this.
Hope this guide/exploit helps someone!