A few months back (basically when I first got my Vilv S5) I had encountered a problem with win7 not rotating the touch screen. Well, finally solution has popped up provided by another user not from Viliv.

http://forum.pocketables.net/showthread.php?p=29555#post29555

We could be waiting forever for Viliv to release some updated drivers. for now this will be the best way to get portrait mode fully supported on the S5.

Now I can really enjoy scrolling up and down some blog websites.