RE: Starsurfer holes on bottom
Just one more clarification - yes, the screws are meant to penetrate, i.e. to enter the holes of the inserts, but not far enough to "penetrate" past the end of the insert and on into the board. As Roger said, the screws seem longer than they should be, but do remember the thickness of the strap and the washer.
Your only other alternative is to drill a hole in the bottom of the centerfin, maybe an inch up from the tip, put a loop of line through it, and then tie the tether line onto the loop. Make sure the knots are tight on the line so you don't lose the board unexpectedly. The downside is that now you have a fin with a hole in it.
Use the strap; it will be the best choice.