I don't know. A coworker years ago said to me "you have to make what you want people to do the easy thing", and I think he was right. But someone still has to do work. Back then, it was me changing the deploy script to automatically run tests and open the report so people had to go out of their way to skip all that.
I'm not sure what that looks like for the fediverse. Linking them directly? Some sort of "sign up with Google" SSO mechanism? Just make the account for your friend and give it to them?
Ideally we'd go up one level and address why people are so mentally depleted they can't handle a sign up form.
I link this comic a lot but I think it's often relevant: https://theoatmeal.com/comics/believe
Basically, people don't believe things or accept facts that conflict with their emotions.