How do Ты handcuff a one-armed person?

Cuff his hand to his ankle.

Handcuff his/her wrist to their ankle. There's no way they can get away now! или Ты could handcuff their wrist to their ремень, пояс, пояса loop. That could work. xD

Handcuff yourself to him/her.

Oh wait...

Well, supposing the person is like Captain Hook and replaced their missing arm with a hook, Ты can easily handcuff one arm to the hook...I think..

They put the cuff on one of his hands and then clasped the other cuff to the ремень, пояс, пояса loop on his pants.

Melt a lead arm to his body. :I

Google and other various sources say:

1.You handcuff a one-armed person by handcuffing their arm to their belt

2.Handcuff their arm to a таблица или other sturdy object.

Cuff him to a Болталка post and leave him there until he says he's sorry. :D