I've bookmarked this thread and will bug you for updates if they aren't regularly forthcoming!
I will as we go along.
First meeting was as much of an evaluation as anything else. I think we determined his capabilities pretty well. We roughed out some possible ideas, curiously I think he was consigned to thinking that shooting over the top of his fist (initially this position crossed the center line of his wrist as well) was an only option. This is not ideal for a variety of reasons, being crossed up during setup, the ability to cue at various heights without altering the level of the cue and the bridging length, overall alignment, etc. I think he had trouble initially wrapping his mind around the idea that we were going to put him an as ideal a position as is humanly possible.
We eventually mocked up a wooden handled wire frame Proto. The concept at this point provides something that he can grasp in his hand so he can really feel like he is actually supporting the cue himself, it has self centering feet that will rotate to find the level of the table, so he won't have to regrip to 'get it right'. These feet also maintain his wrist in a comfortable relationship for him to the table and a the same time offer stabilization when this is sometimes difficult for him to control alone. We are still able have physical contact with the felt which I like myself. Additional concerns will allow these feet/base to accommodate shots partially on/off the rail and breaking options.
Outboard of the handle is the cue rest which will (likely) have two rest heights on a non-concentric spindle that when rotated will provide two more for a total of 4, instantly on demand (this point is still under development and may change) As he plays league regularly, speed and simplicity where very high in the to do list. Others included as small a footprint as possible and extreme ease of use and set up on the fly. This handle/rest combination then allows us to give him a final cue rest position that is nearly identical to the position he would achieve if he had the full use of his hand.
That's where we are at as this point. A functional prototype is the next step so that he can put some table time in and continue to refine the concept from a practical standpoint.
One would have to look closely to be able to tell he has any disability at all when he is down in the shooting the position.
So that's is so far.