Line marker for folded code block

Hi,

I was wondering if it is possible to add a line marker for a code block that has been folded.
I've added line markers from my custom line marker provider, but these disappear as soon as the specific code block is folded. I can see this makes sense, but I would like to be able to show a line marker when the code is folded by my own custom folding builder.
I don't think this can be done by matching on the PSI, as the PSI doesn't change when code is folded. Is there another way to do this?

thanks,
Guno