Custom key combinations in dwm

I have some custom key combinations in config.h, which work great. I just got a 60% keyboard, and would like to config arrows to work vim like ¨hjkl¨, instead of the combination with FN key + arrows.

I tried to use xmodmap but if I define Muhenkan key as a Mode key, it will interfere with the usual behaviour of dwm (mod + J = previous window).

Is there any way I can define: keycode 102 (Muhenkan) + keycode 44 (j) = Down ? Thanks,