On my PepperPad, EUC-KR is already in the encoding options but I found that if I renamed your file EUC-KRenc and added this to Encodings.xml (using an existing line as an example) then an option "EUC-KRenc" appeared in the menu. I could not test that it really worked though.
In any case, please post on FBReader's
Google Group since the developers don't routinely read MobileRead. That way your file can be made part of the standard code base.
By the way, does Mobipocket Reader support Korean?