Well, after my clutch cable shaping a month ago, I ran a new one where the old one was and got up to the handle, on the last step.. spent a total of two hours trying to house the knob into the correct slot. I've been riding it without it fully housed but 'secure' for about the time I was banned. No fraying or issues but I'd really like to house it just for safer measure.

If the line is impossibly too taut [even when adjusted out to the highest allotted slack] to put into it's housing under the clutch lever, are there any tricks to alleviate this issue?

I would remove the bolt-pivot that holds the lever to the base (it has a counter-nut at the bottom and threads into the base), install the cable in the base and lever and only then, relocate the lever (caring for not braking the little plunger of the clutch micro-switch that is under the base) and the bolt-pivot.

Screw the adjustor and lock ring all the way in, then out a bit until the slots in the adjustor and the lock ring are facing forward. With the cable NOT routed through the adjustor, stick the end into the lever. Pull on the housing and sneak the cable into the adjustor via the slot.

No guarantee.