How to control Alpha Cutoff across the length of an object, is that even possible?

I'm starting to understand what's the deal with transparency depth sorting, ie. why it doesn't work right in Unity, or anywhere else, no matter what and that it's a royal pain in the butt and makes me want to throw my laptop through the window...

So now I am looking at the cutout shaders, which apparently don't have these problems. I know I can animate the alpha cutoff value from a script, which is a good start. My gloss map is basically the same as my bump map, so animating the alpha cutoff value makes it disappear from its creases outward, which actually looks cooler than a 'real' alpha fade.

But can I map gray values of an image file to alpha cutoff values in the shader- or more usefully, two separate images that I can blend between?

"/!\ No results found for 'alpha cutoff map'." —The Google

I want to make the object appear and disappear from one end to the other rather than all at once, so I want to map alpha cutoff value A to one end of the U or V axis, and alpha cutoff value B to the other end. Maybe blending ramp images is the way to do it, or maybe scripting within the shader- a prospect which still fills me with dread. Or, does the alpha cutoff value simply Not Work That Way?