OK, so the name is not the best, and the one we ran last night probably needed some better balancing, but the mechanic seemed sound so I thought I'd share it here.
The party, who were none of them magic wielders, were working a ritual to remove a curse from its victim. Rather than a simple "remove curse" spell, the curse was instead drawn out by willfully repeating the incantation.
Mechanically, the party (3 of them) were making Charisma checks against a DC, with each success counting as a "hit" against the victim's Charisma, reducing it by 1. At the same time, the victim was doing the same, with each success offsetting one of the party's successes.
There were no intervening forces, so they were able to focus up. It worked out that the party succeeded in (IIRC) 4 or 5 rounds, inflicting enough "psychic damage" to dispel the curse. However, if the victim had managed enough successes the curse would have been triggered.
Made for a fun encounter, just thought maybe it'll be useful to someone.