I am, believe it or not, becoming more aware of the need for theological musing to be treated as a useful good, as a means to a greater end, rather than as an end in itself. It's a bit tricky, since contemplating God is a good end in itself (the end, in fact, but we're not there yet), and theological musing and contemplating God can swirl together, somewhat like the various stages of lectio divina.
So, for example, the theological musing, "The Father's will needn't necessarily have been the Passion," shouldn't be the end of a line of reasoning. The moral isn't that God could work our salvation in just about any old way, like a magician who can, depending on what he feels like doing, produce the missing card from his pocket or a book on the shelf or the envelope he handed to the volunteer at the beginning of the trick.
Instead, we might continue along these lines: The fact that the Father did will the Passion reveals (or at least hints at) a whole chain or set or design of absolutely free choices. The potential alternate universe in which we (though, as Zippy points out, in another universe "we" aren't us, since we're in fact in this universe) are saved by Jesus picking up a pin isn't something to think about for its own sake, but for what it tells us about God's actual designs for this universe (or, along somewhat different lines, about God's omnipotence).
I'd say it isn't that God could have saved you-as-you-actually-are, as you are actually to be saved, by some means other than Christ's free sacrifice. That idea may well be literal nonsense. Rather, it's that God did save you-as-you-actually-are, as you are actually to be saved, by means of Christ's free sacrifice -- and He didn't have to.
That combination of absolute freedom and the actual choice made is meal enough to chew over forever.