This was how I accomplished this quest for my level 19 gnome twink, without any help from friends or multiple accounts:

1. First, I moved my 70 main and twink out to the arena in STV.

2. Secondly, I logged out my main on the edge of the arena so that he was not in neutral mode and could not be attacked by members of the same faction. I logged out my twink in the center of the arena.

3. I set an alarm for every 3rd hour when the arena starts.

4. Approximately five minutes before the arena started, I logged in my main and sweeped the edges of the arena with perception to catch any horde in the area before the arena even started.

5. When the chest was dropped, I ran into the arena and immediately began opening the chest. If there were any stealthers or other 70s nearby, they would challenge me and I would kill them (most of the time, anyway). After clearing all visible opposition, I opened the chest and took all items but the trinket itself.

6. I jumped on top of the chest and force quit WoW (Alt+f4). This had the advantage of leaving my 70 in the arena for approximately 45 seconds (your main will actually be in-game during step 7), deterring any ninjas or late arrivals from taking the chest. Simply logging out will leave ninjas with an easy grab.

7. I restarted wow and logged onto my twink. Having the advantage of being a tiny gnome female, I was able to actually log inside the chest, being invisible from the outside. If you are a different race, this may be more difficult, but hopefully your 70 main will be enough of a deterrent to allow you enough time to grab the trinket.

8. I logged out my twink, moved my main up to the edge again and waited another 3 hours to do it all over again.

Using this method, I was successful 12 of 14 tries, which is an incredible success ratio considering the amount of competition from both 70s and lowbies. Happy hunting!