you'll need to buy the more expensive roku box which gives you the freedom (if apps are available).
the nowtv box is a roku box locked for sky, who own nowtv, Netflix and Amazon are competitors. what you are asking for is similar to saying to tesco, i like asda and Sainsbury too, can you also have their stores within your stores... not going to happen.
if you want freedom, you'll need to purchase the roku branded box.
