A lot of the motivation for the 1MB limit was a fear that if it weren't limited we'd have people building gigantic blocks just to clog up the system. If someone with major hashing power started building giant blocks every time he got a block, he could DoS the system just by making the block chain too large for most people to store.
How exactly would this be done? Where are these transactions coming from? Could this "bloating" attack be detected and these blocks rejected?
It would be better to prevent this some other way and remove the limit entirely.
It's a simple matter of having the miner send one (or more) of his unspent txouts to a new txout -- which he also controls, of course. He can even put in a generous tx fee -- because he's the miner and he'll collect it. They won't cost him anything even if another miner gets the block. The other miner hasn't heard about them yet (because the guy bloating blocks didn't broadcast them), hence the attacker won't even owe any tx fees.
So, yes, in principle a miner can bloat a block with as many bogus transactions as he wants, it won't cost him a darn thing to do so beyond the possibility that his huge block broadcasts more slowly and gets orphaned, and there's really not much anybody can do to stop him.