How to share a host account...

Hi guys, in a previous message I posted was adviced to share big host accounts (i.e. 100 mb+) with several small host accounts (i.e. 5mb) and understood how to redirect domain names and all that stuff. But, currently I'm looking for a solution to enable every small account to be selfmaintenanced by clients (i.e. file and subdirectory upload, rename, delete, etc.) through web browser (not FTP) using each one its own username and password to access a controlled web space (something like a little control panel, most host companies offers, but with a lot fewer choices)

Thanks in advance for your help.