nginx user directive - multiple users?

Hi,

I'm using nginx as a reverse proxy with apache. I'm using fcgi/mod_fcgi, hence, my php processes run under specific 'users' from each domain on my server.

Example:
site1.com

user = site1

site2.com

user = site2

However, in nginx.conf, I can only use one user. So if I put "site1", then site2 does not work for obvious reasons. Any solutions? Something like

user site1 site2;
or
user site1 || site2;
or
user site1, site2;

Would anything like that work?

For now, I'm running it as nobody and it is working fine but I wonder if that's safe? How about running it as root user? Safe?