Access/Modify LUT in Post-Process Material?

So it sounds like I must be missing something obvious (and I hope that’s the case!).

To clarify: I have no trouble using a post-process material to do a basic change like applying a tint over depth with a custom colour gradient passed as a texture, e.g.,

with the expected results:

.

The trouble I’m having is that I’m not sure how to access or modify the LUT within a material… It doesn’t seem to be exposed, but maybe I’m just missing it?