This is less of a perl issue, and more of an Apache configuration issue, but one key question is:

Which version of Apache are you running?

If it's 2.0, then you might be able to modify your location directive as follows:

<Location /foo>
     DirectorySlash Off
     SetHandler perl-script
     PerlHandler FooModule
</Location>
[download]

This will turn off the mod_dir redirects, even though they should redirect from slashless to slashful (love that word) resources; however, it depends on other configuration directives.

Also, ensure that ServerName has been set explicitly.

Hope this helped,
-v