I have managed to setup a working sample project for you by following your guidelines. You can find it in the attached file (TelerikMvcAppGridTabstrip.zip).
You will notice that I have moved the TabStrip intitialization from the Dialog control to the kendo template, which is used to populate the Dialog. In order to pass the needed data to MyController, I have added a third parameter to the LoadContentFrom() method, in which you can specify the needed data that will be passed to the controller action.
By making the above modifications you will be able to pass the respective row dataItem to the controller and filter it as needed.
I hope this solves your issue.
Telerik by Progress