Thanks for the instructions jackie_w.
Unfortunately, I can't them to work in my slightly different scenario: I am trying to embed fonts in the sblgnt-v1.2.epub online here (
http://katadrew.com/files/sblgnt/) so as to get polytonic Greek displaying on my Sony PRS-T1. Instead of GenBK I used GenR102 and GenI102, but followed the other directions as closely as possible. The Greek text displays in Calibre, but not as Gentium. It is still gibberish on the PRS-T1.
Thanks for any assistance!