Inspired by thawk from hi-pda forum, I found we could actually link *any* font from an epub file.
Just put the following script:
font-family: "Freestyle Script";
in the CSS and put your font at FONT/FREESCPT.TTF of internal storage.
And actually it supports *any* unicode locale. (Fonts on MS is also possible.)
So no more font embedding. There's no 'Formatting' for ePub and it turns much faster than PDFs.