Bear with me, this is going to be tough to word clearly.
Let's say I have a VPS account and I want to resell, and host a bunch of people on my server, giving them their own separate domains. Each user should be able to ftp in and upload files to their domain. The catch here is, Apache likes to run as a single process owner (usually www-data), and this creates a problem. I can check /etc/apache2/envvars to change the user/group to something else, but I need each user to have the proper rights to their own folders. And Apache needs to be set up in a way that the users don't have to set folders/files writable to a certain group in order for PHP to write to them (a la WordPress).
How do I set things up to work this way, for a multi-user shared hosting environment?