Without anyone noticing it. You see, I use a garbage tanking gear set mostly consisting of 174-187 blues that's just barely good enough to clear all heroic dungeons. Whenever a tanking or dps plate item (and neck/rings) drop, I roll need on it. If I get called out on it, I simply show what I'm wearing at the time and its all good.
Why do I do this? It's cause my tank is an enchanter and I can disenchant that stuff and sell it for gold. Great little scheme, isn't it?
I do have a proper tanking set cause I also do raids but I enjoy being a little bastard stealing everything under everyone's nose and getting away with it.
You can always farm some stuff instead of doing dungeons, buy 3 times more reagents you can possibly get with this method, spending the same time on it.
Most people will gladly let you "ninja" like that just to have a tank. The more dungeons you "ninja," the more the community benefits. Thank you for your service.