J.
This Carseat has a unique base to it can rotate towards the parent to make the Carseat face toward the parent. It will still have the strap buttons issue but maybe easier to work with. Should ask their technical department. It is a high priced choice however.
http://www.orbitbaby.com/support/index.html
You should have him visit a Occupational Therapist who might have other options, a Physical Therapist or a Biomedical Engineer. Also consider could he get a big spring type clamp from a hardware store to apply the pressure in a small area which he is having difficulty doing? (like big plastic clamps for holding wood together). Because maybe the father's whole hand could handle the clamp and let the clamp's "fingers" apply the pressure. (as long as the child's little hands and fingers can stay far away from such a clamp)! Also there are Carseat specialists (1-866-Seat Check) that do occasional inspections of carseat installations who could probably offer suggestions. http://www.Seatcheck.org
http://www.orbitbaby.com/support/index.html
Sincerely,
StevenC
Founder BabY-CooP CluB