Issues with Running WordPress as User

I have created a user "user". This user has the directory /home/user. His WordPress website is in the /home/user/public_html directory.

I have created a sftp jail for him with the instructions here. That works well.

Now, "user" wants to update a WP plugin. However, he cannot b/c the /home/user/public_html is owned by "user" and not www-data.

What is a solution to this problem?

Debian 7.0 32 bit Nginx v 1.4.4 Php fpm v 5.5 via Dotdeb