Accessible Superscripts: PowerPoint to PDF

I've been asked to make 4,000 PowerPoint slides into PDFs that are accessible to the vision-impaired.  Many of them contain simple math expressions, like 2⁸ - 1.  If I make the superscript using the font controls in PPT, Adobe Read Out Loud reads this as "twenty-eight [pause] one."  Putting in a Unicode superscript 8 (U+2078) changes the way Read Out Loud interprets punctuation like bullets elsewhere on the page and anyway doesn't read the superscript correctly.  If I assign alternate text, the alternate text is read, but also "twenty-eight..."  Surely there is a way to fix this, preferably within the PPT so that I don't have to touch each PDF page.

A Unicode superscript two is read as "superscript 2," but that doesn't appear to work in general.  In any case, I really want "two to the eighth" rather than "two superscript 8" if possible.  (Superscripts 1, 2, and 3 are part of ISO 8859-1; higher superscripts are Unicode only.)

I am working with PowerPoint 2010 and Acrobat X Pro.  I do not have access to JAWS, NVDA, or other screen reader programs.

Help will be appreciated.