Hmm..I see your point there
Be darned if I knew how do it without hurting the spar...unless you happen to find a suitably modifiable 'bit' in the hardware store I reckon soldering would probably be the best course.

You could always make a 'bracket in a bracket' (perpendicular to each other i.e. one around the spar to hold down the other thats in line with the ribs) but that would probably be rather clumsy and too much fiddling about...

If this were a semi-scale project, then I'd suggest you install some aluminium ribs with the attachments built in.
Maybe we should just wait for donny's wing and all will become clear