Probably best to just submit a patch. See patch/create in patch(1).
Ah, I don't finish to check it's ok for other keyboard layout, such as ascii etc. Then, I wanted to send it to the usb keyboard driver's author.
Original kb.c uses its value of transformed PS2 scan code, which is not applicable to such OADG 日本語109 keyboard. Then, I changed it to use the usageID to check whether it has two bytes code or not.