Deleting performances that have been used in packages

I wonder if you guys can help me - yes; I'm in a pickle once again.

I've had to set up dummy performances (long story, but the short version is that Management wanted sales to be taken before all of the details about the new Facility were known). Happily, however, we got those details before we went on sale (the onsale date got pushed back) - but after the dummy performances were set up.

In the interests of cleanliness, I'd rather these performances were deleted without trace: obviously, no bookings have been taken, so now's the time to do it. However, when I go to delete the performances in Production Elements, I get the following message: "This performance cannot be deleted because it has been used in performance groups."

Now - this is true. But no bookings have been taken, the affected performance group has been deleted and removed from the package of which it was a part. I'd really, really like these dummy performances deleted.

Is this possible?

C.//
X.