Just thought I would chime in here -- Our solution does currently implement a solution for this which may or may not be useful to you.
version = HttpContext.Current.IsDebuggingEnabled ? DateTime.Now.ToString() : FileVersionInfo.GetVersionInfo(Assembly.GetExecutingAssembly().Location).FileVersion;
And it's usage is:
You'll need to import the namespace into your .aspx file, though:
<%@ Import Namespace=
What this does is appends to the end of a path either the current Date/Time in Debug mode, or the solution's version in Release mode. What this means for you as a developer is that in Debug mode this file will not be able to be cached. Then, out in the wild, every time you release a new version of your product -- the old cache will be replaced with new, but not again until a new version.
I would still recc. keeping your RadStyleSheetManager on the page, though, as it does do additional work in condensing all the files into one request.