I think the short answer is that this is not directly doable.
But for Mathematica there is no direct Powerpoint export. You can however export the various elements (graphs, etc...) to formats that you can then import to Powerpoint.
Another approach is to put your Mathematica notebook in the Slideshow screen enviornment and then Save the notebook As a PDF. Then from inside Powerpoint you can Insert as Picture and select the page of the PDF to go into a slide. You will have to do this page-by-page. I am not sure how this will turn out, but it's worth a try.
Of course the better option if at all possible is to use Mathematica, especially if you have interactive content to show--it would wow your interviewers...