I've had success with the wire girdle method on maples but it has not worked on a few conifers. The iso alcohol idea is interesting and will certainly give it a shot.
Just for clarification, there is the wire turniquet applied to the tree in lieu of girdling the tree. Harry Harrington of Bonsai4me recommends this for some species. I've tried it on JBP. It does work, induces awesome basal flare, but takes at least one extra season. George Marakana, a grower in Nepemo, CA has tried it versus girdling and found this as well.
On the other hand, some people are of the opinion that a bridged girdle is because the top of the girdle growing downward. They espouse what Al has done, also wrap a wire around the top edge of the girdle to deflect the growth from the top of the girdle outward. This is what I am not convinced of and haven't really ever tried simply because the argument is not sensible to my experience. Obviously, I think residual cambium is the reason. The iso wipe down seems to do the trick.
BTW, I've attached a photo of a bald cypress girdle showing the growth of residual cambium after a few weeks - an instance of when I tried to scrape all the green away. The point is just to support my view of how bridging occurs, though I did subsequently cut this growth away, do the iso wipe, and had the layer root successfully. As I said previously, I've not had any of these troubles when doing the iso wipe as part of the original process.