UserDir + Alias = suexec not being invoked

[Zachary Palmer <zep_apache_httpd_list@xxxxxxxx>]

All,

I have an Apache HTTPD instance I am trying to configure for a fairly 
small group of users.  We're using mod_userdir and mod_suphp to ensure 
that user scripts are run as the users themselves rather than as the www 
user.

My objective is to configure the website in such a way that certain 
distinguished portions of the site can be made easier to access.  For 
instance, I would like

     http://mysite.com/~foouser/barsite

to be equivalent to

     http://mysite.com/bazsite

To this end, we have the following subset of configuration:

<VirtualHost *:80>
<Directory /var/www/>
             Options Indexes FollowSymLinks MultiViews ExecCGI Includes
             AllowOverride None
             Order allow,deny
             allow from all
</Directory>
<Directory /home/*/public_html>
             Options ExecCGI MultiViews Indexes SymLinksIfOwnerMatch 
IncludesNoExec
             AllowOverride All
<Limit GET POST OPTIONS>
                 Order allow,deny
                 allow from all
</Limit>
<LimitExcept GET POST OPTIONS>
                 Order deny,allow
                 deny from all
</LimitExcept>
             Order allow,deny
             allow from all
</Directory>
         Alias /bazsite /home/foouser/public_html/barsite
         UserDir public_html
         UserDir disabled root
         # ... more stuff here ...
</VirtualHost>

Unfortunately, this does not permit suexec to do its job; in fact, it 
seems that suexec is never used.  A script 
/home/foouser/public_html/barsite/test.py is executed correctly if 
accessed via the URL

     http://mysite.com/~foouser/barsite/test.py

but, when accessed via the URL

     http://mysite.com/bazsite/test.py

the script runs as the www user rather than as foouser.  I would not 
have expected this, since it doesn't meet my intuitions about aliasing.

Clearly, these alias directories need not be generative; they will be 
assigned on a case-by-case basis.  Does anyone know how I would express 
to Apache that scripts in a specific subdirectory (recursively downward, 
of course) should always be executed by suexec to a given user?

Thanks!

Zach