[Zope] starting zope with su instead of -u

[Dylan Reinhardt]

This feels like a huge newbie question, but I'm starting to lose hair
and I was surprised not to find anything helpful in the archives.

I want to try out DirectoryStorage.  I gather you're not supposed to use
the -u option and obviously I don't want to run as root.

So I use something like

su - -c START_COMMAND zope

But then I get that message about how I can't run zope as root and
should read the SETUID doc.  But I'm not running zope as root and the
SETUID doc is distinctly unhelpful with respect to using anything other
than -u to drop privileges.

Is there something basic I'm missing? 

I'm running 2.6.1 on Gentoo, if it matters.

Thanks in advance,

Dylan