It's referred to as" friends and family" accounts. Usually limited to about 10 I think. With account size limits of 100k max. Haven't looked into it in years.
Try amp futures
or ninjatrader brokerage. they have or had a deal going thru oanda.
I couldn't find any mention of it on their site; but will shoot them an email and ask.
Thanks
I think ATC brokers offers such services and is available for US residents.