Every Upwork user can set up a freelancer profile and a client profile within their same account.
Very important: There is only one account. Same username. Same password. Same email address.
Log in at the same time. But switch between the "client" and "freelancer" aspects of the account.
Technically what you do is create a "client company."
What I do is just make it clear in the message room that I'm outsourcing. I've actually never outsourced anything but got invites for things where I can do some of it but felt more comfortable having someone else do other parts and made it clear that's what I would be doing.