Setting DOCROOT from a variable passed with PASSENV

Hi,

I am trying to setup a dynamic httpd.conf file. Essentially I pass in
a user variable from the owner of the httpd process.

Ex. PassEnv VARIABLE_FOR_DOCROOT_PATH

Then I'd like to use this path as my DocRoot

DocRoot ${VARIABLE_FOR_DOCROOT_PATH}

Is this allowed? Wha tis the correct syntax?

steve