However a quantum machine that would be capable of post-selection is described by the more powerful class PostBQP = PP, and we know that PP includes NP, so this justifies your analogy.
I don't know much about quantum physics or quantum computing, so I may be mistaken, but it seems to me that post-selection is more of a philosophical construct than something that is physically possible, though.
I've seen post-selection demonstrated in a laboratory. It definitely isn't just a philosophical construct, except inasmuch as what it says about time making people want it to be less than real, and logic doesn't work that way.
As for whether you could make a PostBQP-capable computer, though.. I don't think so, at least in the most general case. I don't understand this nearly well enough to be sure, but from what I've heard, tricking causality like that has the problem that you're increasing the chance of your circuitry failing right along with the chance of getting the right result, and quantum computers are already hard enough.
The latter of which is exactly what a quantom computer does. The problem is that when we make a measurement, we randomly select one of the execution paths and see its result. The problem is that once we make a measurement, we would have to repeat the experiment in order to make another measurement.
How sure are we that BQP != NP?