We currently accomplish this with zero-width spaces plus a trigger that fires on "copy" in Paste and Diffusion. This is quite gross.
In the new-style Harbormaster logs, we use an approach that seems slightly better: CSS psuedoelements.
Use it in Paste/Files/Diffusion too.
This gives us good behavior in all browsers in Files and Paste.
This gives us good behavior in Chrome and Firefox in Diffusion. Safari will copy (but not visually select) blame information in Diffusion. I think we can live with that for now.