Izriul from Laughing Skull made an interesting post on the official forum, how to kill Gold Sellers with the Shaman Fire Nova Totems (see the original post here). The basic idea is, that totems become neutral for a splitsecond, once their owner logs off just before they disappear. If you time the Fire Nova Explosion for the brief periods where the totem will be neutral it will deal damage to allied players.
Testing it I found out that it works best for me to type /camp, but not to hit enter until yata (yet another totem addon) shows 1.6 seconds remaining. Then I hit enter and will be logged out a few miliseconds later, leaving my neutral totems on the ground. Depending on your latency it should work roughly the same for you.
I put up a short demonstration video (5mb) for you: