Either SDC or Impulse (both download programs) is the only way you'll get the patches. They did this to help curb pirating I believe, since your SDC/Impulse needs the serial for the game to DL.
Stardock's programs aren't invasive like other companies' products. They don't need to connect to the internet via them to run the game. Open up SDC/Impulse, get your updates, don't open it up/connect to the internet again until you wish for more updates. Heck, you could even uninstall it after getting the update for all it matters.