I've used an adjustable stem, previously. A Ritchey 4-axis adjustable (click @ Ritcheylogic.com); this one's an example of a stem for the AheadSet standard. Works fine. Take it apart, lock it down, and it's set. It's got big splines inside the unit that aren't going anywhere once you tighten the adjustment screw. Very solid. Indistinguishable from a typical non-adjustable stem, function-wise, other than it adjusts in angle. There are less-expensive adjustable stems made, but the Ritchey is a well-designed one.

As others have said, similar units are available out there for quill-type stems.

I've used it and kept it, in some cases. And I've used it to dial-in the fit, then swapped it for the correct stem (angle and length). Works fine, either way.

Am currently building-up a bike that has an uncut steerer on the fork, which extends a good foot above the head tube. Using numerous spacers, I'm able to raise the height of the existing stem to the height where the bars will result in "perfect" hand position. Once I've determined the right spot (for the hands), I'll get a stem with the appropriate angle and length (likely, shorter and much steeper), then cut off the "excess" from the steerer tube. (Right now, the length of the steerer tube is ludicrously tall, but that's only for testing/fitting purposes and temporary.)