Well, if you're not allowed to read the file, you're pretty much stuck, aren't you? :-)
PHP usually runs with very restricted permissions, for obvious reasons; if it's an Apache module, then Apache's are the permissions it runs with - and do you want every man and his dog to be able to poke through your logfiles?
If you've compiled PHP as a CGI, you could write the script and run it from the command line as a user that does have permission to read the logfiles.
This is the sort of job Perl was invented for...