but most people won't have this module installed...
Installed, or loaded? I know the httpd.conf defaults to having that module commented out, but the module itself should be around.
Maybe relying on Apache::Session would cover more install scnerios instead. I was trying to avoid writing a custom handler just to accept and toss some cookies in the test environment, but maybe that's better. At least then everyone install should be able to run the A-T cookie test.