Unfortunately I'm not sure that there's much else to be done other than Wide Window and Trim Lines. Although you could add line breaks in your list source, which means handling the whole selection somehow. I did something like this in my vimdex macro, though that was really to handle multiline-single sections in my source list, and it may or may not be more effort than its worth.
It probably wouldn't be very difficult to replace the Prompt With List action with a Custom HMTL Prompt action which can allow for much wider window frames. Is that of interest to you?
I have to say that, for UX, this isn't good. It's easy to spot differences at the start of a line. More difficult, but still doable, at the end of a line (especially when, as here, the ends line up).
But trying to spot differences in the middle of a line of text? Nah...
Is there any way you can reformat what the prompt is showing so that the differences are more obvious? "Friendly" values can be useful for this, letting you show one thing but return another.
Well, then try running the following action. It will create a list of items in a window and when the user double clicks on an item, a KM variable called SelectedItem is set to the string that the user clicked on.
This is a demonstration. I didn't address all your requirements in this demonstration, like the window's height or width. I just wanted to hear from you if this kind of solution is interesting to you. And I'll be honest, I just asked ChatGPT to write the code, which is how I write most Custom HTML code.