Hey if you can find a way for that ability to work without rolling the open, that is awesome.
I think it is cheating to limit the ability with a play style that completely prevent a player from using the ability.
I think cheating is a pretty strong word for a popular style of play. I'm still a fan of the threshold method, as Netopalis states.
As the OP and having just made a Dual-cursed Oracle/Paladin, I find myself not using misfortune much at all.
The parties I was in just never seems to need it. They would ether kill all the monsters way too quickly or we would face creeps that are out of range for my misfortune...
I only managed to get it off once on a critical hit on a fellow player. (Most GMs say it out loud on a critical.)
Makes me wonder why some players even bother with it other then to keep asking the GMs to show them their rolls... :P