I'm fixed. As I don't have any other content on this webserver besides shindig, I realized I didn't need to use .htaccess (which was, for reasons yet unknown, not being referenced).
I put the Rewrite* directives into my httpd.conf and after modifying the value of cache_root to a priv'ed directory, allowing CacheStorageFile to create in the directory, I was able to load the sample remote ToDo gadget.
