We need good hashrate proxy software first. I'm not aware of any. We need to build it.
Discussion
The DATUM gateway software allows you to partially do this, in that you get insight into whether your miners are connected and can choose to set minimum diff *higher* and/or drop sending worker names to the pool. You can't set min diff between the miner and the gateway *lower* than the pool diff, but that would be a natural extension.
Ocean does it right. Love those guys. They've got some very cool stuff coming out soon.