actually, it is possible. The Inquisit Player defaults to landscape to maintain consistency, but the behavior can be overridden by the canvas.
To lock in portrait mode you need to specify a canvas that has a larger height than width.
For Portrait on iPad/iPhone:
<defaults>
/ canvasaspectratio = (3,4)
</defaults>
Or whatever you feel is appropriate. It can also be accomplished using "/ canvassize" with appropriate sizes.
For Portrait on iPad/iPhone:
<defaults>
/ canvassize = (99%,100%)
</defaults>