At minimum he can be put into overalls making it harder to get to the diaper and those are available for any age.

You will have some success putting on a tshirt that is way big over his clothes - sort of like putting him in a dress. When he is sitting he will then be sitting on the shirt and it is harder to get it up high enough to get the hands in - at least it buys you some time.

A real pain for diaper changing since you need to totally remove everything but once had a child who was such a problem that we put a girl's bathing suit on him - served the purpose of a onsie and again all sizes available and if necessary get one second hand yourself and put it on him over his clothes as soon as he arrives.