With help of jackie_w and JSWolf if found an easier solution:
Just add this lines to the css file in the epub:
Code:
@font-face {font-family: serif; font-weight: normal; font-style: normal; src: url(res:///ebook/fonts/AmasisMTW1G.otf)}
@font-face {font-family: serif; font-weight: normal; font-style: italic; src: url(res:///ebook/fonts/AmasisMTW1G-Italic.otf);}
@font-face {font-family: serif; font-weight: bold; font-style: normal; src: url(res:///ebook/fonts/AmasisMTW1G-Bold.otf);}
@font-face {font-family: serif; font-weight: bold; font-style: italic; src: url(res:///ebook/fonts/AmasisMTW1G-BoldItalic.otf);}
The book will be automatically displayed right!