No matter what reward method is used, when a pool is down to zero buffer on a long round, it must either underpay or create debt for the pool owner. That is an inevitable fact of pooled mining. Nothing can stop it. *MPPS attempts to mitigate it by offering to make up for the loss later.
This is only true for PPS systems. If you do something like the PPLNS that Meni and I have talked about, the variance is pushed to the miners, and not the pool owner. Discarding transaction fees (as most pools do) you will get exactly what you deserve over the long run, with no worries about being underpaid or about the pool owner going bankrupt.