My father in his mid-70's is planning to visit me (I am in the US) and plans to fly Lufthansa. He is in reasonably good health and can walk etc just fine. However he suffers from essential tremors (see here and here) which makes his hands shake and he pretty much can't write anything anymore.

Is there any assistance program available either on board or otherwise to help elderly passengers to fill out US customs and immigration forms? Most of the information I found had to do with reduced mobility etc. and my dad can walk just fine and doesn't really need a wheel chair. He is also fluent in English so he doesn't need assistance with language/translation. What I am looking for is some way he can have someone fill out those forms for him either in Frankfurt or in flight and he will check the yes/no boxes and sign the forms.

I suppose I could fill out those forms myself and mail him and all he does is sign them (btw- is it even legal for me to do so?). I fly a fair amount and have an international trip planned before his, so it's easy for me to grab a few extras.

I guess I am looking at some sort of equivalent to the unaccompanied minor programs except for the elderly.

Any pointers will be greatly appreciated.