I am afraid that we're stuck with it. From the above link.
Printed publications use a special “BPS” family of fonts. These feature the Pali diacritical characters (such as a-macron or m-dot-below) mapped to the lower 256 character positions. It was necessary to create these fonts because our publishing software (Framemaker® 5.5.6 or Pagemaker® 6.5 or 7.0) do not support Unicode. The BPS encoding is shown below.
I suppose I could offer to reformat the book for them in PagePlus or LibreOffice, but its not a small undertaking even if they would agree to it.