Victor at The Dead Parrot Society offers his variation on a plan to restore actuarial balance in the social security system by adjusting the indexation provisions of benefit formulas. A riff on a proposal by Robert Pozen, the essential idea is to maintain wage indexation at the lower end of the benefit-income distribution, while shifting toward CPI-indexation-only for everyone else (on a sliding scale).
What Progressive CPI-Indexing does is to let the current system of benefits work for the lower income classes. In Pozen's version, the bottom 30% of the wage earners in 2012 (and beyond if the wage distribution doesn't change) will get the exact same scheduled benefits that they get now. The very, very top of the income distribution will have their benefits frozen at a constant real level. People in between will fall, well, somewhere in between.
Mechanically, Pozen suggests that a new "bend point" should be created between the two that already exist. To the left of the "bend point", the formula wouldn't change at all. To the right of the new "bend point", the increase in benefits associated with additional income would be reduced by a proportion designed to freeze the benefit levels of a "steady maximum earner" at a constant real level.
That's really all there is too it. For workers just above the 30th percentile (and therefore just above the new bend point), little would change. For workers at the highest income levels, their benefits would be frozen. Over time, the shape of the benefit curve will change.
If you haven't been following reform proposals based on adjustments in benefit-indexation, Victor's post is a great place to start.