Hi vsrnt, Unfortunately there isn't really a way to do this stock, because that would require integration of your email clients emails with Method, which isn't doable. The best approach I can think of to accomplish this would be to have google gadget installed, then through the gadget manually create a case for every new support email. That's typically what we do here at Method. It's probably possibly to build some implementation of that using our Method API, but that's a higher level of development.
Alternatively, you can have customers submit support tickets through the customer portal, as that is what it was built to achieve.