Remove Sites from Notification List

Hi,

I had a couple test sites that I used during development of our main site. I installed the WPMU Dev Dashboard on these sites. Now the sites are gone so I want to delete them from the "Update Notifications Sites" list, but all I can do is "Disabled" them.

How can I delete these sites from the list? (I really hate leaving loose ends like this)

Thanks,
Rhek