What about a "rename filespace" command, followed by a "delete
filespace" command. Once you rename the filespace, the nightly incremental
will be required to do a full backup. Once that is done, or even a few days
later, you can delete the old filespace.
        You could automate it so that when you rename the filespace, it has
the date in it, so you are sure you are deleting the correct one.

Ben