Miners could voluntarily, do a small fractional amount of pool hopping,
For example, with BfgMiner, I can set up 5 Pools to mine at regular intervals, eg 1 hr each, or 1day each.
If 4 of those were the same pool and 1 were a different pool, then this would reduce my hashing power being sent to a big pool by 20%
They probably wouldn't lose very much if anything by this method, they might get lucky for that period and earn more.
They could even strengthen the network by making one of those pools a P2P pool.
Miners can voluntarily make a difference to the 51% problem.
Not that I'm mining very much with my 1.3 MH Gaw Scrypt Zeusminer