I went to the range this evening, and these videos definitely helped a lot. I was previously using a "thumbs off" grip, and it definitely helped tremendously to keep my thumbs closer to the gun, pointed forward. The second video also helped a lot: using these folks' "leverage" technique makes getting the support hand in place much easier and faster, as well as more secure. And while doing all this, I also discovered a major problem in my grip: my strong hand palm wasn't covering the backstrap enough. My control noticeably improved by the end of the range session.
Thanks gain for linking a great set of videos and letting us know about these fine folks. Heck, I might even visit them for training one of these days if they can relate quality instruction this well!