One of the things that held me back from going the BPW route was the perception of a lack of adjustability. I was at a LDS one day and the guy there showed me how he had his set up. I bought a 2nd hand plate a wing & some webbing and set mine up like his and after some minor tweaking all I can say is that it works slick! It is not in the truest sense of the word "Hogarthian" (although, considering that my last name actually is Hogarth, I guess the argument could be made that any way I rig it would be "Hogarthian".)
Anyways, notwithstanding my name, here is how I have mine rigged. It starts at the shoulders the same way you would with any BPW.
The difference is that instead of running the main webbing through the bottom of the Back Plate, I have taken another piece of webbing about 12-18 inches long (in my case, this is the black webbing) and threaded that through the Back Plate, put a D-Ring on it and secured it with a tri-glide. I then ran my main webbing through the D-Ring from behind.
The D-Ring allows the main webbing to move freely through it and it can instantly either be snugged as tight as needed or loosened as much as needed depending on if you are getting into it (loosen it off) or getting ready to dive (pull it nice & snug).
This may not be an ideal solution for everybody, but for me, It works very well. Admittedly, it does introduce two potential points of failure that otherwise wouldn't be there, but I can get in and out of it just as fast as someone with a BCD that has shoulder clips.
I don't know if this will meet your needs or not, but I thought that I would share.