As pointed out in the comments, this is not correct (even though it comes from Technet - go figure), but Exfolders, formerly known as PFDAVAdmin, does provide this functionality.
With PowerShell, it's pretty easy.
This example grants Ayla Kol read permission to Tony Smith's mailbox.
Add-MailboxPermission -Identity "Tony Smith" -User "Ayla Kol" -AccessRights ReadPermission
You can either write a little script to find team leaders and their team members to feed into that cmdlet, or if your environment's a small one, you could always just do it manually.