Thanks for the instructions.
I tried them, but the opt.fs was about 9MB. The font I used was "Baekmuk gulim" as stated. The font file itself was about 9.90MB itself. (most of the asian .ttf are quite big also)
I got the following messages when trying to write to the device
Info for partition Fsk
Device: 1, start sector: 0x9e, image size: 0x700000
UpdateCreatePartitionWithImage: data is bigger than partition!
I also noticed the following statement in the instructions.
>Total size of opt.fs file must be less than 7 MB.
How to build an image < 7MB?

May be I missed some important steps?
Cheers!