I'm not entirely sure about the boxed version being able to that Vern, someone will have a better idea.
However, it often appears as a bundle, often with most DLC at a very reasonable price. In fact, this one just ended a few days ago.
http://www.bundlestars.com/all-bundles/ ... bundle+mpuIt will come around again most likely or it will be on Steam for a low price. I've even seen the base game pop up at places such as GreenManGaming for as little as £2.49 so my advice would be to just hang fire, you'll be able to buy it again for cheap.