hi sloppy-jo,
yes there is an implement you can buy - i work in a chemist and we order specifics such as this for customers - any good chemist will have a catalogue of these kind of aids and they should order in for you. it's a kind of hoop on a stick, over which he will put his sock and then he will put his foot thru and it then pulls on. he will be able to do this from his seated position.