I think I found my answer User Defined Encodings You can also add new encodings to the set that FontForge knows about. There are three menu items that manipulate a set of user defined encodings. As always these specify both a character set and an encoding. The encoding has a maximum of 256 entries, but the character set may be larger (up to 1024). This means that you can define a font with extra characters. Since postscript fonts can be reencoded at runtime this can be useful. The Load Encoding command...
Ethiopic Enccoding