One way to solve this is to host on a Windows server instead of Unix based. Windows is inherently case-insensitive, Unix the opposite. One work-around might be to set up PHP redirects. To do that you'd have to set up directories for each variation you wanted to catch. E.g.
Then in the "dummy" director(ies) put an index.php something like:
header( 'Location: http://www.example.com/ClientName/index.html' ) ;
The site address has been entered incorrectly. If your browser does not automatically redirect you, please click <a href="../ClientName/index.html">here</a> to continue...
Note: You must NOT precede this with ANY code, not even a blank line.
P.S. There are a number of other ways to redirect users, but I use PHP because:
a) It is handled by your server, so is not dependent on the user's browser.
b) It does not require changes to the server's htaccess file.
c) Using the HTML <meta> redirect is frowned upon.
See http://www.wikihow.com/Redirect-a-URL for details of other ways...