I'd recommend the spacer-on-top-of-the-stem approach, it's going to be the safest way to go. Especially with forks as light as those. I also like their plug; the lip on the end means there's no ambiguity about where it should be located, and if someone does get aggro about clamping their stem onto the end of the carbon tube, the plug's lip will help keep the stem from deforming/cracking the steertube.