That's every SIMILAR to how I did it with the fretless. In that instance I cut a vertical slot (different stage of the neck, much more carved). Here I drew a line at 1 cm depth on the side of the neck, set the fret saw to 5 mm cutting depth and cut at an angle. Should work just fine but the lines will be a lot shorter (which doesn't bother me, they'll be clearly visible).
Requires a little bit of forward thinking but I personally think it's a great way of achieving acceptable accuracy on a fretless without ruining the board (thank you, Ivan, for agreeing with that).