Haha! That's kinda funny. Logs full of blocked porn sites from your workstation... I understand why you wouldn't want that history in there. Though it might be fun explaining to the CIO that it was "For Science!" 😉
If this is really a problem then I'd suggest cloning a new network based on your current settings, move the MX over there, do the testing, then move it back and delete the network. Event logs are network specific so if you do your testing in a dummy network that's been deleted there will be no trace of them going forward.