Developing a Flex Response is a bit more involved than just providing a simple command string. I'd look to find a qualified, authorized partner who could develop this for you, or sell you something they may have already developed for this. Sounds like a simple flex response, but in reality even something this simple is going to take a non-trivial amount of time to develop.
Recommendations:
(1) Use the quarantine function as described above, then purge the quarantine directory regularly (effectively deleting these files but only after having moved them somewhere else).
(2) Use some sort of batch processing using a list of file locations from DLP (all incidents where the file last accessed date is greater than 2 years old, for instance).
(3) Wait for Symantec to build this into DLP if you already know that it's on their roadmap.
~Keith