3pcs Mobility Independence Kit: Portable Standing Aid,Car Grab Handle Auto Cane,Adjustable Standing Aid Safety Handle,Liberty Lift Assist Suitable for Elderly, Disabled and Pregnant,Convenient Travel

Since he can bridge up and has decent arm function, I'd look into an extra hook for your car that he can use as a handle and he could probably just bridge and pivot without the sliding board. Here's some links https://a.co/d/01uuVz8P https://a.co/d/0bso6wLl https://a.co/d/0isrsZ4m (swivel seat cushion)