Reply to master clock button flash with tempo

so theres a fairly useless button (to me) on the s4 that i believe could be repurposed. what if i had the master button (in between SNAP and QUANT) flash with the beat of the master clock, i would find that extremely usefull.
how could i do that. any way to set the brightness of it to 0, then have another controll flash it, (like ean shows how to)

thoughts?