anti-splog rename signup page causes issues when deleted blog is requested by another server

I have the option to rename the signup page in antisplog settings so direct access to wp-signup.php wont work.

I have a feed fetching service which is activated for all new blogs and it attempts to periodically access the sites feed to update it's record.

The problem is that after I've deleted a blog for being a spammer, the feed service still tries to access the blog at it's normal feed address. If a blog is deleted, wordpress tries to redirect to the main blog signup page at domain.com/wp-signup.php?new=oldblogname which, of course, isn't allowed with the option to rename the signup page enabled in anti-splog.

It's only showing a 404 with a simple message but with a few hundred requests going through that process, it literally kills the server. I've attached an image which shows the server load difference after I banned the IP of the feed fetching server from trying to access mine.

is there a more graceful way to 404 the request to the signup page in anti splog?