If there isn't sufficient material to drill for 6M, (and if you have enough clearance, and can approach from the right angle) you could insert an ultra-low profile cap
screw from the back side, and put a nut on it to pinch the cable. I can't tell from the photo whether it will be possible, but it's fairly likely, I think.
[edit] link didn't seem to go through correctly, but they're under stainless cap screws...
