Static preview url & allow regular expressions in root path

I use url rewriting on my site. Now when i click on "preview" it tries to display the current file under the root path (url) which, of course, doesn't work.

It would be great if i could

a) set a fixed url when i click preview (f.e: always domain.com/, with no filename at all)
b) teach coda how my url rewrite works (how to translate filenames to path)

Example: current filename is "something_different.php" and with regexp i could tell coda that the preview url is "/something/different/"

Well.. these are actually two ideas, but either would work for me while the latter is probably the most satisfying.

Once regexp is working people could start sharing expressions know to work for common frameworks (wordpress, code igniter, cakephp, zend, rails, etc.).