XP - ATTACKS/SKILLS TARGETING SP INSTEAD OF HP - HOW TO DO?

Basically, please see title. I'm working out some of the steps for my battle structure, and this is one of the points I'm unsure of how to handle. I'd thought I'd seen a post on the topic on HBGames at one point recently, but I can't find it now.

To reiterate: How would I set it up (what scripts would I need to modify, or add) so that I can mark skills and weapons that remove the target's MP/SP instead of the target's HP?