Ian, bolting right through is without doubt a better solution than the studs I have just suggested, but less easy to implement as a retro fit.

My concern with the ally threads, is more about how they age, than their initial strength which although I dont like the concept of, I accept that they no doubt ARE strong enough initially.
With a stud, the thread stays strong for a lot longer if its being adjusted a lot, especially if there is the risk people doing it up arent using a torque wrench etc, it just seems more "idiot proof" that way round.

Your solution is (of course) a technically better one though