I like that idea of using a condition (instead of a character style). That might stand out even more. You would also need to enable “show and print” in the Conditional Text panel, so that the condition “wavy lines” appear in the PDF.

Thank you, Michel, for the ~I. grep… I did not read the original question carefully enough. Yes, this grep would work great.

One way might be to adjust where the first baseline of the text starts. In Object > Text Frame Options, click Baseline Options.

Understanding the First Baseline Position of Text

It won’t work in an EPUB. Interesting that it doesn’t work in Publish Online. I believe it should work with in5.
I wonder if it works with this script:

Exporting from InDesign to HTML5: Amazing Free Script

I haven’t seen that, but I do know there are some good index utilities at the following links:
https://creativepro.com/files/kahrel/indesign/lists_indexes.html
and
https://www.kerntiff.co.uk/products-4-indesign/indexutilities