I don't know if you can. Shale Hill doesn't run with Ren'py, instead it uses its own customized engine which means that CGs and other assets probably aren't as easily accessible.
I thought I saw a mention in this thread, or maybe the parallel thread that had a cracked "5.?" version in it, that noted pulling images from .dat files (which is what I believe SHS is using). I did a search, and I believe it's what they based the "Unren" tool upon. It's basically just a command/procedure that unwinds the procedure used to create the .dat files from the .jpeg or .png files to begin with.
I'm no longer very technical, but it didn't seem to be difficult - just a matter of identifying the proper files and using the proper tool/process. I came up with decent search terms pretty quickly that got me results, but I don't recall what they were (this was about 2 or 3 months ago - I've slept and killed brain cells since then).