I do the same thing. I also use the Camaleon package (github.com/SublimeText/Camaleon) to be able to hit F8 and switch between color schemes. I prefer a light theme here at the office (lots of harsh overhead lights) and a dark theme at home (low lighting).
I did do one trick though - I love the context menu and you don't get that if you don't install the app. So, I first installed ST2 normally into it's Program Files location. This also enabled the context menu. I then deleted the contents of "C:\Program Files\Sublime Text 2" folder and all its contents. Then I just created a symlink (mklink /d [Link] [Target]) to the location I keep my portable version of ST2 on Dropbox. So Windows thinks ST2 is installed
I'm sure there are easier ways to accomplish the context menu, but I was in a hurry and that's what worked.