I'm willing to accept that you can't see it being viable, but I'm still not seeing *why* you think that.
Three reasons:
Out-of-universe, it's too easy a fix; the White Court just aren't able to live as "normal people".
In-universe, if this was possible, why didn't Harry build something like this for Thomas when he was fighting his Hunger between BR and TC? Even if Harry didn't know enough about the Hunger's nature, Lara does; why didn't she suggest Harry do thaumaturgy to feed raw magic to Thomas' Hunger in PT?
In-universe, it doesn't really fit the way the feeding is described to work IMO. It's been described as merging auras with the prey. I think it needs an actual coherent aura/spirit of a sentient living being*, not just "X quantity of life-magic energy".
*Maybe a close-enough-to-mortal being ... we've seen it used on part-humans in "Backup" and "Bigfoot on Campus", but never on totally-inhuman things. Kind of doubt it would work on Bob or Kalshazzak or an Outsider.
Your take is that they need to feed on raw spiritual energy, which has been shown to be compatible with being bottled (belt buckle).
Not quite. I think
what is being consumed is "generic" life force energy - not specifically fear energy or lust energy. But the
mode of access to that energy isn't compatible with anything other than a near-human being... an item can't work since the item itself doesn't have a spirit or experience emotion.
Like it's just a method for them to stoke the spirit and open the tap of the victim.
Basically, yeah... Thomas' Hunger demon can eat his own life force directly. So the emotions provide
access to energy not energy itself.
It's not like a person has separate stores of "lust energy" and "fear energy" and "despair energy" and so on. A person has a certain amount of life force, and there are different ways to access it. (Wizards & other spellcasters can draw on their own life force, sometimes using emotions, sometimes not.)
Someone drained to zero by the White Court dies; they don't become dispassionate or fearless or whatever. And in "Bigfoot on Campus" we see that a being with more life energy than the Hunger Demon can handle can survive a normally-fatal feeding. That pretty much confirms that it's "life force" not specifically "emotion type" energy.