The man wants MORE caster. How about this idea?
With the parallel suspension's inherent design flaws, I have to think bump steer is a bigger problem than the hair splitting geometry we are discussing at this point.
Sure, toe change (bump steer) is more important for controlling the car than how you actually go about measuring the toe. As long as you measure the toe in a way that's consistent and repeatable it's fine. There are pretty well established standards for measuring it fractionally or by degrees, and even online calculators to convert between the two if you need. Really that just comes down to if your tires are going to wear correctly and the car will drive straight.
And it still depends on what you're doing with the car, a street car should pretty much always have toe-in because it's easier to control. Less focus on toe-in for a drag car, you want just enough to offset the play in the steering system so you're running at zero toe down the track because that's the least rolling resistance. For AutoX, and less so for road tracks, some folks will set a little toe out, because it makes changing directions a smidge faster. But on the street it would feel flighty and loose.
I just think it's important to understand what toe is, so you're not confusing how it's measured with what the actual purpose is. And that's totally splitting hairs, absolutely.
Regardless, measuring static toe for an alignment is the same if you've got -1° caster or +10° caster, like I said earlier. That actual caster setting will affect the toe change curve, but so will the ride height and a lot of other things. And whether that caster setting improves or degrades the toe change curve on a given car would depend on the rest of its geometry.