I have sent you a WAO assembly via direct message. To implement your custom exclude filter you will need to inherit from the MonoSoftware.Web.WAO.Handlers.CssHandler
and override the following method:
OnOptimizing(HttpContext context, CancelEventArgs e)
Here you can put your custom exclude filter and cancel the optimization for current request.
Let us know if this has helped you so we can sign off this task.