An interesting article, Rawiri. Well done.
I am reminded of Aristotle's doctrine (which I paraphrase here), "virtue is in moderation." I.e., that any trait is a virtue only in the proper amount. Thus, one can have a vice (as you noted) either both in being too impatient or in being too patient. What is "moderate," I assume, depends upon the trait and the circumstance; I'm sure that we would all be considered disastrously impatient by men of the middle ages, but such is merely what today's world demands of us.
Thus, it comes down to the individual to judge what is the proper level that produces a "virtue" of a given trait, in any given situation. While impatience can often be a "virtue" of sorts, one will inevitably encounter a situation in which being impatient is detrimental to ones goals; same with patience.
So to "channel" our vices to good, we shouldn't "encourage" them to become more extreme than they are, but instead develop them to the point where they can be "turned on and off" and moderated at will. If a situation demands impatience, a magician will not let an idle moment pass; if it demands patience, he could sit there all day. Ultimately, it isn't the goal of the magician to be "virtuous" and "without vices" per se, but rather to be able to place himself above the level of such personality-based impulses altogether, and act according to higher ideals and reasons.