I later realized that padding to 32 bytes didn't make much of a difference, it is the number of vacuous NOP opcodes generated that matters. So it can be simplified to

    mov rcx, 400000000-1
    up:
    nop
    nop
    nop
    add [counter], rcx
    nop
    nop
    nop
    dec rcx
    nop
    nop
    nop
    jnz up
    ret

which probably works fine for the majority of decoding methods, be it MITE, LSD, or DSB.