If you want a very fast-and-loose hack, treat the character's emotional strength/weakness as a Duty per AoR, but rather than gaining it via goals, they gain it any time their emotional strength/weakness comes into play in a dramatic fashion, regardless of how it actually resolves. (Succumbing to the emotional weakness is just as valid as overcoming it!)
You don't have any ranks or the like associated with it in this case, but some minor perk related to their strength/weakness can occur when it hits 100 and resets.
And whether they're light or dark is entirely dependent on the narrative.
Ideas on alternate Conflict and Morality systems
I'm a big proponent of Maelora's Strength/Passion system. It's the one I use, and it takes numbers out of the equation and makes the most important thing the character, and their actions. However, it can be seen as a bit disconnected from the setting, as it's intended to allow you to explore all aspects of the character without penalty, which some people don't like as much. But I'll share it below, for those interested!
The general idea is that there are four "stances" your Force-sensitive character can be in at any one time:
--Light Paragon:
Gain +2 Strain Threshold while in this stance, and FLIP one Dark Side Destiny Point to Light Side when entering this stance and at the start of every encounter in this stance. Use white pips on Force dice to generate Force points, but may pay the normal costs to access black pips. Use Force powers/talents as a Light-side character. Cannot use Conflict talents or powers unless you are paying the cost to use black pips from Force dice.
--Light:
Use white pips on Force dice to generate Force points, but may pay the normal costs to access black pips. Use Force powers/talents as a Light-side character. Cannot use Conflict talents or powers unless you are paying the cost to use black pips from Force dice.
--Dark:
Use black pips on Force dice to generate Force points, but may pay the normal costs to access white pips. Use Force powers as a Dark-side character.
--Dark Paragon:
Gain +2 Wound Threshold and -2 Strain Threshold while in this stance, and ADD one Dark Side Destiny Point to the pool when entering this stance and at the start of every encounter in this stance. Use black pips on Force dice to generate Force points, but may pay the normal costs to access white pips. Use Force powers as a Dark-side character.
How you determine which stance you're in at any one time is dependent on play and the actions your character takes. Each character chooses either Light or Dark to be their default. At the end of downtime (like a hyperspace trip, resting, timeskips, etc.), or when your character has a few moments to stop and center themself, they revert to their default stance if they're not in it. If they are in Light stance, by taking repeated actions, or actions strongly associated with the Dark side (or if events happen that would trigger them to feel strongly Dark emotions), they change to Dark stance. The inverse is also true - a character that is in Dark stance that acts in ways aligned with the Light, or who experience events that would make them feel in "Light-side" ways can change to Light stance.
Each group, and even every character, would have different calibration to how sensitive this is.
To get into either of the Paragon stances, you have to be acting in a way that strongly aligns with your Emotional Strength or your Emotional Passion (re-name for "Weakness," as in this system it's not intended to be a flaw but rather a different side of your personality; although the character may themselves see it as a personal flaw). For instance, if your Strength is Courage, doing an action that is highly courageous at great risk to yourself would put you in Light Paragon stance. If your Passion is Anger, lashing out and causing destruction that will have major and/or lasting repercussions on yourself and others would put you in Dark Paragon stance.
The Paragon stances rarely last long; if you're acting Courageously, you'll probably finish your heroism during that encounter, and return to normal Light stance afterwards. A fit of Anger-induced rage will often burn out and be stopped (or snapped out of) fairly quickly, and so on. However, if you can maintain it for multiple encounters, the effect on the Destiny Pool continues to accumulate. Do note that the action (flip/add) has been inverted, though.
And finally, if a character changes significantly in how they behave, or their personal outlook, or their relationship/understanding of the Force, they can change their default stance, permanently switching from default Light to default Dark, or vice-versa.