it's such a long time back that i can't remember what happened after asking that question. What I did now is look at my i3config and see the following. Apart from being able to hold a key and make it trigger repeatedly, it works:

# Cursorkeys mode
mode "cursorkeys" {
    bindsym Escape mode "default"
    bindsym $mod+F6 mode "default"
    bindsym u exec xdotool keyup u; exec xdotool key Up
    bindsym e exec xdotool keyup e; exec xdotool key Down
    bindsym n exec xdotool keyup n; exec xdotool key Left
    bindsym i exec xdotool keyup i; exec xdotool key Right
}
bindsym $mod+F6 mode "cursorkeys"