Another option you didn't mention is for the customer to consider issuing a power of attorney to a trusted family member or friend who could help him out. He could also appoint an authorized signer to the same end. Your banker may have offered those solutions to the customer, along with the others you described, but perhaps the customer isn't yet ready to take a step that he might feel diminishes his self-image or is an admission of his diminished physical capacity in some way.
It's probably not wise to try to nudge your customer into taking any of these steps. If he finds that he really needs to do something, he'll act.
One cautionary bit of advice: bank personnel should not offer to assist this customer in completing his checks, however well-meaning they might be.