I have a client who has a hosting arrangement with 400 customer sites all hosted through SuPHP in CGI mode on Apache. The sysop is now gone and the client is calling on me for rolling out a new PHP thing. Trouble is -- server load is very high right now and we have found that it's due to the crawlers. We had one customer in particular who complained of slow websites, and we engaged a 304 header plugin in his site against most crawlers, and his site perked right up.

We'd like to lower that load by issuing a global 304 header to all the crawlers, letting human visitors through. I have a long list of user agent keywords to trap for.

What's the best way to temporarily engage that global 304 header, while allowing human visitors to get right on through?

I mean, I could roll out 400 .htaccess file changes, but it would be ideal to make this change in like one central Apache config and then it automatically affect all the sites at once.