Another point of view.  Remember 'assignment of income?'

I have a big brokerage account.  I put my GF as co-owner.  [Don't tell my wife!]

I did not file 709.  Maybe GF does not even know.

I go back to: "Whose $$ is it?"  If they truly own it equally, report income equally.  But I do not see how you can shift income to whomever wants it each year.

show it as a nominee distribution

You asked Twice, new one is here:

https://accountants-community.intuit.com/questions/1825704-i-have-co-owners-of-a-brokerage-account-w...

I will close the older duplicate.