We've got a CentOS/Apache server with a ton of "content providers" that only have write access to specific directories. In our case, we use ACLs to grant access to the specific parts of the /var/www/html tree. If there's only one or two users, we usually add individual ACL entries for each, if there's a herd[1] of them we set up a group, make them members, and set the ACLs to use the group. I'm surprised nobody brought it up already!
[1] users come in herds, like all forms of cattle.