A friend of mine takes his adult son out in a wheel chair. He has an 18' stanley center console, and puts his son up front, just ahead of the console. Works fine. It takes 2 strong guys to get him aboard, and you need a launch with a good dock.
I'm not sure you'll have the space, or freeboard to be safe in a ranger.
If its rough, don't even try it.
Pick a good day with stable weather. Its totaally doable, just be smart about it and pick a good day.
Good on you for getting him out!
S.