No you really can't. I'm serious. I've fully BM'd 6 characters at level 50 now and I've never, ever, ever not gotten a medal, except one time that I joined *right* as the warzone was ending before I even got out of the spawn. Either I'm a pro (I'm not) or it's just really not that hard.
You can if you stick to the objectives and put the team ahead of personal gain. If you play for medals --- great for you ... but there are some people out there that concentrate on doing what needs to be done for the team to have a chance even when it's futile. Like it or not, it does happen.
Is getting no medals common? Not for good players obviously, but nobody just jumps in and is good vs premade Warlord teams using voice chat. Losing is fine and part of the process, but there is no reason why someone that does accomplish objectives in a WZ should not have at least 1 medal since medals are all important.