Tim Heuer figured out the right stored procedure to modify in Subtext 18.104.22.168 to disable tracking of referrals altogether. I'm all for this since it means less need to monitor my database and remove/shrink the referral table.
I updated my Subtext Database Maintenance page so you can fix your DB up with a single click. Enable/disable, push-button style. All yours, free, YMMV. Do note that it does actually modify the stored proc, so if you've got your DB locked down or you've customized stuff, this may not be something you want to do. You have been warned.