Multiple Postfix Instances

I'm a little short on hardware with a start up venture and I want some
redundancy on my mail server. I'm going to have to go live with a
preliminary configuration and make some changes, like adding VERP,
later. I've had plenty of fun before with users of a hobby system
growing disgruntled when mail was out for 3 days. Now I'm going to be
running some commercial applications as well, and I'm hoping to avoid
losing any mail when I modify configuration files

Has anyone tried running multiple Postfix instances as described in
this How-To?

http://advosys.ca/papers/postfix-instance.html

Are there any particular security issues involved in this? The How-To
uses an environment variable to control which set of configuration
files are referenced when calling the mailq program for outbound mail.
Will that work with 2.4 or 2.5rc2? Trusting the environment is not
behavior that I expected from Postfix.

Chris