Didn't really get that far with this one, but the only thing that immediately occurs to me that doesn't run afoul of the idea that each Primary Stat represents two opposed concepts, would be handing out advancement points in those three flavors depending on what it's earned for. You could assign the gain to either of the linked Secondary Stats (and probably have a trickle-down effect to the skills like in YAPPIE/YIPPIE/YORKIE/whatever name it is this week) after applying it to the Primary Stat, but not the other two Primaries or their linked Secondaries.

--
"Okay, I got your henshin pen from Lu- er - from the top-secret Moon Cave, so here it is!" Usagi chirped. "Just hold it up and say the first thing that comes to mind!"
"This feels really stupid," Ranma deadpanned.
The pen shot a few raspberry colored sparks and made a rude noise. - R1/2&SM: No Henshin (unwritten)