Custom usage info in Find Usages tool window and popup

I'd like to customize the usage info shown in the Find Usages tool window or popup. I already implemented a custom UsageTypeProvider to show my own text on the first level, e.g. "Usage in XXX", but I'd like to customize the concrete usage info, too.

Here's an example to hopefully make it clear what I'm trying to achieve:

Found Usages
-> Usage in XXX (already customized via UsageTypeProvider)
  -> my.package.name
    -> myFile.xml
      -> 1 <?xml version="1.0" encoding="utf-8"?>

I'd like to customize the package, file, and file content info in this tree. Is this possible at all? And if it is, how do I do it?

Thanks, Victor