Friendly URLs with path but without first level

Hi together,
since years i love friendly URLs and the possibilities to get a path structure with FURLs. But in my case it’s needed to jump over the first level:

[tt]
- MODx
-- startpage -> /index.html
- subpage -> /index/subpage.html should called /subpage.html
- subfolder -> /index/subfolder.html should called /subfolder.html
-- subpage -> /index/subfolder/subpage.html should called /subfolder/subpage.html
-- servicefolder -> siteservice (hidden folder)
- page -> /siteservice/pageXYZ.html should called /pageXYZ.html
[/tt]

And: No, it’s not possible to move the pages one level up!

Do You have an idea what i have to do to change FURLs to work in this way?

Perhaps a custom mod_rewrite rule?