I think there are two possible ways to achieve that. First one is by the blog post you have mentioned. I created a new file "CustomProvider" that will extend the dynamic module provider. Here is my CustomProvider.cs
CustomProvider : OpenAccessDynamicModuleProvider
It is required to check the content type of your item because the provider is common for all of the dynamic types. Build your solution, open Administration -> Settings -> Advanced -> DynamicModules -> Providers and create a new one. Set Title and Name to any value. For ProviderType enter your type, in my case SitefinityWebApp.CustomProvider, save and restart your application. You can see my settings here:
Then create some items in that provider and in the dynamic widgets change the provider property as shown in the blog post (you should have provider selector when the widget is opened for edit). Now by opening details view of the items urls should be with the correct format.
Another solution for that problem might be to create a page named "Cars" and make the dynamic content widget redirect to that page. I have recorded a short video demonstrating that -> http://screencast.com/t/2Q4xTVOvZP
I would like to mention that the trick with providers will work for Sitefinity versions after 5.2 while for 5.1 and before only the workaround with pages will work.
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